[PATCH V3 0/2] Add support to configure DWC for ECRC

[PATCH V3 0/2] Add support to configure DWC for ECRC

[Vidya Sagar]

This series has two patches.

Patch-1: Adds a public API to query if the system has ECRC policty turned on.

Patch-2: DesignWare core PCIe IP has a TLP Digest (TD) override bit in one of
its control registers of ATU. This bit needs to be programmed for proper ECRC
functionality. This is currently identified as an issue with DesignWare
IP version 4.90a. DWC code queries the PCIe sub-system through the API added
in Patch-1 to find out if ECRC is turned on or not and configures ATU
accordingly.

V3:
* Addressed Ethan Zhao's comments for patch-1

V2:
* Addressed Jingoo's review comments

Vidya Sagar (2):
  PCI/AER: Add pcie_is_ecrc_enabled() API
  PCI: dwc: Add support to configure for ECRC

 drivers/pci/controller/dwc/pcie-designware.c |  8 ++++++--
 drivers/pci/controller/dwc/pcie-designware.h |  1 +
 drivers/pci/pci.h                            |  2 ++
 drivers/pci/pcie/aer.c                       | 11 +++++++++++
 4 files changed, 20 insertions(+), 2 deletions(-)

-- 
2.17.1

[PATCH V3 1/2] PCI/AER: Add pcie_is_ecrc_enabled() API

[Vidya Sagar]

Adds pcie_is_ecrc_enabled() API to let other sub-systems (like DesignWare)
to query if ECRC policy is enabled and perform any configuration
required in those respective sub-systems.

Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
Reviewed-by: Jingoo Han <jingoohan1@gmail.com>
---
V3:
* Address Ethan Zhao's comments
* Added 'Reviewed-by: Jingoo Han <jingoohan1@gmail.com>'

V2:
* None from V1

 drivers/pci/pci.h      |  2 ++
 drivers/pci/pcie/aer.c | 11 +++++++++++
 2 files changed, 13 insertions(+)

diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index fa12f7cbc1a0..325fdbf91dde 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -575,9 +575,11 @@ static inline void pcie_aspm_powersave_config_link(struct pci_dev *pdev) { }
 #ifdef CONFIG_PCIE_ECRC
 void pcie_set_ecrc_checking(struct pci_dev *dev);
 void pcie_ecrc_get_policy(char *str);
+bool pcie_is_ecrc_enabled(void);
 #else
 static inline void pcie_set_ecrc_checking(struct pci_dev *dev) { }
 static inline void pcie_ecrc_get_policy(char *str) { }
+static inline bool pcie_is_ecrc_enabled(void) { return false; }
 #endif
 
 #ifdef CONFIG_PCIE_PTM
diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
index 65dff5f3457a..d0f5a7043aff 100644
--- a/drivers/pci/pcie/aer.c
+++ b/drivers/pci/pcie/aer.c
@@ -207,6 +207,17 @@ void pcie_ecrc_get_policy(char *str)
 
 	ecrc_policy = i;
 }
+
+/**
+ * pcie_is_ecrc_enabled - returns if ECRC is enabled in the system or not
+ *
+ * Returns true if ECRC policy is enabled and false otherwise
+ */
+bool pcie_is_ecrc_enabled(void)
+{
+	return ecrc_policy == ECRC_POLICY_ON;
+}
+EXPORT_SYMBOL(pcie_is_ecrc_enabled);
 #endif	/* CONFIG_PCIE_ECRC */
 
 #define	PCI_EXP_AER_FLAGS	(PCI_EXP_DEVCTL_CERE | PCI_EXP_DEVCTL_NFERE | \
-- 
2.17.1

[PATCH V3 2/2] PCI: dwc: Add support to configure for ECRC

[Vidya Sagar]

DesignWare core has a TLP digest (TD) override bit in one of the control
registers of ATU. This bit also needs to be programmed for proper ECRC
functionality. This is currently identified as an issue with DesignWare
IP version 4.90a. This patch does the required programming in ATU upon
querying the system policy for ECRC.

Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
Reviewed-by: Jingoo Han <jingoohan1@gmail.com>
---
V3:
* Added 'Reviewed-by: Jingoo Han <jingoohan1@gmail.com>'

V2:
* Addressed Jingoo's review comment
* Removed saving 'td' bit information in 'dw_pcie' structure

 drivers/pci/controller/dwc/pcie-designware.c | 8 ++++++--
 drivers/pci/controller/dwc/pcie-designware.h | 1 +
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
index b5e438b70cd5..cbd651b219d2 100644
--- a/drivers/pci/controller/dwc/pcie-designware.c
+++ b/drivers/pci/controller/dwc/pcie-designware.c
@@ -246,6 +246,8 @@ static void dw_pcie_prog_outbound_atu_unroll(struct dw_pcie *pci, u8 func_no,
 	dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_UPPER_TARGET,
 				 upper_32_bits(pci_addr));
 	val = type | PCIE_ATU_FUNC_NUM(func_no);
+	if (pci->version == 0x490A)
+		val = val | pcie_is_ecrc_enabled() << PCIE_ATU_TD_SHIFT;
 	val = upper_32_bits(size - 1) ?
 		val | PCIE_ATU_INCREASE_REGION_SIZE : val;
 	dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_REGION_CTRL1, val);
@@ -294,8 +296,10 @@ static void __dw_pcie_prog_outbound_atu(struct dw_pcie *pci, u8 func_no,
 			   lower_32_bits(pci_addr));
 	dw_pcie_writel_dbi(pci, PCIE_ATU_UPPER_TARGET,
 			   upper_32_bits(pci_addr));
-	dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, type |
-			   PCIE_ATU_FUNC_NUM(func_no));
+	val = type | PCIE_ATU_FUNC_NUM(func_no);
+	if (pci->version == 0x490A)
+		val = val | pcie_is_ecrc_enabled() << PCIE_ATU_TD_SHIFT;
+	dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, val);
 	dw_pcie_writel_dbi(pci, PCIE_ATU_CR2, PCIE_ATU_ENABLE);
 
 	/*
diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
index e7f441441db2..b01ef407fd52 100644
--- a/drivers/pci/controller/dwc/pcie-designware.h
+++ b/drivers/pci/controller/dwc/pcie-designware.h
@@ -89,6 +89,7 @@
 #define PCIE_ATU_TYPE_IO		0x2
 #define PCIE_ATU_TYPE_CFG0		0x4
 #define PCIE_ATU_TYPE_CFG1		0x5
+#define PCIE_ATU_TD_SHIFT		8
 #define PCIE_ATU_FUNC_NUM(pf)           ((pf) << 20)
 #define PCIE_ATU_CR2			0x908
 #define PCIE_ATU_ENABLE			BIT(31)
-- 
2.17.1

Re: [PATCH V3 2/2] PCI: dwc: Add support to configure for ECRC

[Jingoo Han]

On 10/29/20, 1:40 AM, Vidya Sagar wrote:
> 
> DesignWare core has a TLP digest (TD) override bit in one of the control
> registers of ATU. This bit also needs to be programmed for proper ECRC
> functionality. This is currently identified as an issue with DesignWare
> IP version 4.90a. This patch does the required programming in ATU upon
> querying the system policy for ECRC.
>
> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> Reviewed-by: Jingoo Han <jingoohan1@gmail.com>

No, it should be Acked-by. I gave you Acked-by, not Reviewed-by.

Acked-by: Jingoo Han <jingoohan1@gmail.com>


Best regards,
Jingoo Han

> ---
> V3:
> * Added 'Reviewed-by: Jingoo Han <jingoohan1@gmail.com>'
>
> V2:
> * Addressed Jingoo's review comment
> * Removed saving 'td' bit information in 'dw_pcie' structure
>
>  drivers/pci/controller/dwc/pcie-designware.c | 8 ++++++--
>  drivers/pci/controller/dwc/pcie-designware.h | 1 +
>  2 files changed, 7 insertions(+), 2 deletions(-)

[...]

Re: [PATCH V3 2/2] PCI: dwc: Add support to configure for ECRC

[Vidya Sagar]

On 10/30/2020 3:33 AM, Jingoo Han wrote:
> External email: Use caution opening links or attachments
> 
> 
> On 10/29/20, 1:40 AM, Vidya Sagar wrote:
>>
>> DesignWare core has a TLP digest (TD) override bit in one of the control
>> registers of ATU. This bit also needs to be programmed for proper ECRC
>> functionality. This is currently identified as an issue with DesignWare
>> IP version 4.90a. This patch does the required programming in ATU upon
>> querying the system policy for ECRC.
>>
>> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
>> Reviewed-by: Jingoo Han <jingoohan1@gmail.com>
> 
> No, it should be Acked-by. I gave you Acked-by, not Reviewed-by.
> 
> Acked-by: Jingoo Han <jingoohan1@gmail.com>
Apologies. My bad. I saw the 'Reviewed-by' of the other patch (i.e. 
PCI/AER: Add pcie_is_ecrc_enabled() API) and put that for this patch as 
well. I'll update.

> 
> 
> Best regards,
> Jingoo Han
> 
>> ---
>> V3:
>> * Added 'Reviewed-by: Jingoo Han <jingoohan1@gmail.com>'
>>
>> V2:
>> * Addressed Jingoo's review comment
>> * Removed saving 'td' bit information in 'dw_pcie' structure
>>
>>   drivers/pci/controller/dwc/pcie-designware.c | 8 ++++++--
>>   drivers/pci/controller/dwc/pcie-designware.h | 1 +
>>   2 files changed, 7 insertions(+), 2 deletions(-)
> 
> [...]
> 

Re: [PATCH V3 2/2] PCI: dwc: Add support to configure for ECRC

[Rob Herring]

On Thu, Oct 29, 2020 at 12:40 AM Vidya Sagar <vidyas@nvidia.com> wrote:
>
> DesignWare core has a TLP digest (TD) override bit in one of the control
> registers of ATU. This bit also needs to be programmed for proper ECRC
> functionality. This is currently identified as an issue with DesignWare
> IP version 4.90a. This patch does the required programming in ATU upon
> querying the system policy for ECRC.
>
> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> Reviewed-by: Jingoo Han <jingoohan1@gmail.com>
> ---
> V3:
> * Added 'Reviewed-by: Jingoo Han <jingoohan1@gmail.com>'
>
> V2:
> * Addressed Jingoo's review comment
> * Removed saving 'td' bit information in 'dw_pcie' structure
>
>  drivers/pci/controller/dwc/pcie-designware.c | 8 ++++++--
>  drivers/pci/controller/dwc/pcie-designware.h | 1 +
>  2 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> index b5e438b70cd5..cbd651b219d2 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.c
> +++ b/drivers/pci/controller/dwc/pcie-designware.c
> @@ -246,6 +246,8 @@ static void dw_pcie_prog_outbound_atu_unroll(struct dw_pcie *pci, u8 func_no,
>         dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_UPPER_TARGET,
>                                  upper_32_bits(pci_addr));
>         val = type | PCIE_ATU_FUNC_NUM(func_no);
> +       if (pci->version == 0x490A)
> +               val = val | pcie_is_ecrc_enabled() << PCIE_ATU_TD_SHIFT;
>         val = upper_32_bits(size - 1) ?
>                 val | PCIE_ATU_INCREASE_REGION_SIZE : val;
>         dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_REGION_CTRL1, val);
> @@ -294,8 +296,10 @@ static void __dw_pcie_prog_outbound_atu(struct dw_pcie *pci, u8 func_no,
>                            lower_32_bits(pci_addr));
>         dw_pcie_writel_dbi(pci, PCIE_ATU_UPPER_TARGET,
>                            upper_32_bits(pci_addr));
> -       dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, type |
> -                          PCIE_ATU_FUNC_NUM(func_no));
> +       val = type | PCIE_ATU_FUNC_NUM(func_no);
> +       if (pci->version == 0x490A)

Is this even possible? Are the non-unroll ATU registers available post 4.80?

Rob

Re: [PATCH V3 2/2] PCI: dwc: Add support to configure for ECRC

[Vidya Sagar]

On 11/2/2020 7:45 PM, Rob Herring wrote:
> External email: Use caution opening links or attachments
> 
> 
> On Thu, Oct 29, 2020 at 12:40 AM Vidya Sagar <vidyas@nvidia.com> wrote:
>>
>> DesignWare core has a TLP digest (TD) override bit in one of the control
>> registers of ATU. This bit also needs to be programmed for proper ECRC
>> functionality. This is currently identified as an issue with DesignWare
>> IP version 4.90a. This patch does the required programming in ATU upon
>> querying the system policy for ECRC.
>>
>> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
>> Reviewed-by: Jingoo Han <jingoohan1@gmail.com>
>> ---
>> V3:
>> * Added 'Reviewed-by: Jingoo Han <jingoohan1@gmail.com>'
>>
>> V2:
>> * Addressed Jingoo's review comment
>> * Removed saving 'td' bit information in 'dw_pcie' structure
>>
>>   drivers/pci/controller/dwc/pcie-designware.c | 8 ++++++--
>>   drivers/pci/controller/dwc/pcie-designware.h | 1 +
>>   2 files changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
>> index b5e438b70cd5..cbd651b219d2 100644
>> --- a/drivers/pci/controller/dwc/pcie-designware.c
>> +++ b/drivers/pci/controller/dwc/pcie-designware.c
>> @@ -246,6 +246,8 @@ static void dw_pcie_prog_outbound_atu_unroll(struct dw_pcie *pci, u8 func_no,
>>          dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_UPPER_TARGET,
>>                                   upper_32_bits(pci_addr));
>>          val = type | PCIE_ATU_FUNC_NUM(func_no);
>> +       if (pci->version == 0x490A)
>> +               val = val | pcie_is_ecrc_enabled() << PCIE_ATU_TD_SHIFT;
>>          val = upper_32_bits(size - 1) ?
>>                  val | PCIE_ATU_INCREASE_REGION_SIZE : val;
>>          dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_REGION_CTRL1, val);
>> @@ -294,8 +296,10 @@ static void __dw_pcie_prog_outbound_atu(struct dw_pcie *pci, u8 func_no,
>>                             lower_32_bits(pci_addr));
>>          dw_pcie_writel_dbi(pci, PCIE_ATU_UPPER_TARGET,
>>                             upper_32_bits(pci_addr));
>> -       dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, type |
>> -                          PCIE_ATU_FUNC_NUM(func_no));
>> +       val = type | PCIE_ATU_FUNC_NUM(func_no);
>> +       if (pci->version == 0x490A)
> 
> Is this even possible? Are the non-unroll ATU registers available post 4.80?
I'm not sure. Gustavo might have information about this. I made this 
change so that it is taken care off even if they available.

> 
> Rob
> 

RE: [PATCH V3 2/2] PCI: dwc: Add support to configure for ECRC

[Gustavo Pimentel]

On Mon, Nov 2, 2020 at 14:27:9, Vidya Sagar <vidyas@nvidia.com> wrote:

> 
> 
> On 11/2/2020 7:45 PM, Rob Herring wrote:
> > External email: Use caution opening links or attachments
> > 
> > 
> > On Thu, Oct 29, 2020 at 12:40 AM Vidya Sagar <vidyas@nvidia.com> wrote:
> >>
> >> DesignWare core has a TLP digest (TD) override bit in one of the control
> >> registers of ATU. This bit also needs to be programmed for proper ECRC
> >> functionality. This is currently identified as an issue with DesignWare
> >> IP version 4.90a. This patch does the required programming in ATU upon
> >> querying the system policy for ECRC.
> >>
> >> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> >> Reviewed-by: Jingoo Han <jingoohan1@gmail.com>
> >> ---
> >> V3:
> >> * Added 'Reviewed-by: Jingoo Han <jingoohan1@gmail.com>'
> >>
> >> V2:
> >> * Addressed Jingoo's review comment
> >> * Removed saving 'td' bit information in 'dw_pcie' structure
> >>
> >>   drivers/pci/controller/dwc/pcie-designware.c | 8 ++++++--
> >>   drivers/pci/controller/dwc/pcie-designware.h | 1 +
> >>   2 files changed, 7 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> >> index b5e438b70cd5..cbd651b219d2 100644
> >> --- a/drivers/pci/controller/dwc/pcie-designware.c
> >> +++ b/drivers/pci/controller/dwc/pcie-designware.c
> >> @@ -246,6 +246,8 @@ static void dw_pcie_prog_outbound_atu_unroll(struct dw_pcie *pci, u8 func_no,
> >>          dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_UPPER_TARGET,
> >>                                   upper_32_bits(pci_addr));
> >>          val = type | PCIE_ATU_FUNC_NUM(func_no);
> >> +       if (pci->version == 0x490A)
> >> +               val = val | pcie_is_ecrc_enabled() << PCIE_ATU_TD_SHIFT;
> >>          val = upper_32_bits(size - 1) ?
> >>                  val | PCIE_ATU_INCREASE_REGION_SIZE : val;
> >>          dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_REGION_CTRL1, val);
> >> @@ -294,8 +296,10 @@ static void __dw_pcie_prog_outbound_atu(struct dw_pcie *pci, u8 func_no,
> >>                             lower_32_bits(pci_addr));
> >>          dw_pcie_writel_dbi(pci, PCIE_ATU_UPPER_TARGET,
> >>                             upper_32_bits(pci_addr));
> >> -       dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, type |
> >> -                          PCIE_ATU_FUNC_NUM(func_no));
> >> +       val = type | PCIE_ATU_FUNC_NUM(func_no);
> >> +       if (pci->version == 0x490A)
> > 
> > Is this even possible? Are the non-unroll ATU registers available post 4.80?
> I'm not sure. Gustavo might have information about this. I made this 
> change so that it is taken care off even if they available.

The Synopsys DesignWare PCIe IP is highly configurable, therefore is 
dependable on what the design team has configured for their solution.
Although Synopsys doesn't recommend the use of non-unroll ATU, the 
customers are free to select what they want for their design.

-Gustavo

> 
> > 
> > Rob
> > 

Re: [PATCH V3 2/2] PCI: dwc: Add support to configure for ECRC

[Rob Herring]

On Mon, Nov 2, 2020 at 9:12 AM Gustavo Pimentel
<Gustavo.Pimentel@synopsys.com> wrote:
>
> On Mon, Nov 2, 2020 at 14:27:9, Vidya Sagar <vidyas@nvidia.com> wrote:
>
> >
> >
> > On 11/2/2020 7:45 PM, Rob Herring wrote:
> > > External email: Use caution opening links or attachments
> > >
> > >
> > > On Thu, Oct 29, 2020 at 12:40 AM Vidya Sagar <vidyas@nvidia.com> wrote:
> > >>
> > >> DesignWare core has a TLP digest (TD) override bit in one of the control
> > >> registers of ATU. This bit also needs to be programmed for proper ECRC
> > >> functionality. This is currently identified as an issue with DesignWare
> > >> IP version 4.90a. This patch does the required programming in ATU upon
> > >> querying the system policy for ECRC.
> > >>
> > >> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> > >> Reviewed-by: Jingoo Han <jingoohan1@gmail.com>
> > >> ---
> > >> V3:
> > >> * Added 'Reviewed-by: Jingoo Han <jingoohan1@gmail.com>'
> > >>
> > >> V2:
> > >> * Addressed Jingoo's review comment
> > >> * Removed saving 'td' bit information in 'dw_pcie' structure
> > >>
> > >>   drivers/pci/controller/dwc/pcie-designware.c | 8 ++++++--
> > >>   drivers/pci/controller/dwc/pcie-designware.h | 1 +
> > >>   2 files changed, 7 insertions(+), 2 deletions(-)
> > >>
> > >> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> > >> index b5e438b70cd5..cbd651b219d2 100644
> > >> --- a/drivers/pci/controller/dwc/pcie-designware.c
> > >> +++ b/drivers/pci/controller/dwc/pcie-designware.c
> > >> @@ -246,6 +246,8 @@ static void dw_pcie_prog_outbound_atu_unroll(struct dw_pcie *pci, u8 func_no,
> > >>          dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_UPPER_TARGET,
> > >>                                   upper_32_bits(pci_addr));
> > >>          val = type | PCIE_ATU_FUNC_NUM(func_no);
> > >> +       if (pci->version == 0x490A)
> > >> +               val = val | pcie_is_ecrc_enabled() << PCIE_ATU_TD_SHIFT;
> > >>          val = upper_32_bits(size - 1) ?
> > >>                  val | PCIE_ATU_INCREASE_REGION_SIZE : val;
> > >>          dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_REGION_CTRL1, val);
> > >> @@ -294,8 +296,10 @@ static void __dw_pcie_prog_outbound_atu(struct dw_pcie *pci, u8 func_no,
> > >>                             lower_32_bits(pci_addr));
> > >>          dw_pcie_writel_dbi(pci, PCIE_ATU_UPPER_TARGET,
> > >>                             upper_32_bits(pci_addr));
> > >> -       dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, type |
> > >> -                          PCIE_ATU_FUNC_NUM(func_no));
> > >> +       val = type | PCIE_ATU_FUNC_NUM(func_no);
> > >> +       if (pci->version == 0x490A)
> > >
> > > Is this even possible? Are the non-unroll ATU registers available post 4.80?
> > I'm not sure. Gustavo might have information about this. I made this
> > change so that it is taken care off even if they available.
>
> The Synopsys DesignWare PCIe IP is highly configurable, therefore is
> dependable on what the design team has configured for their solution.
> Although Synopsys doesn't recommend the use of non-unroll ATU, the
> customers are free to select what they want for their design.

Okay, then there's a bug in the driver if the version is set to 0x480A
or later and non-unroll is used:

if (pci->version >= 0x480A || (!pci->version &&
       dw_pcie_iatu_unroll_enabled(pci))) {

Probably can just drop the version checking. The detection should always work.

Rob

RE: [PATCH V3 2/2] PCI: dwc: Add support to configure for ECRC

[Gustavo Pimentel]

On Mon, Nov 2, 2020 at 21:16:52, Rob Herring <robh@kernel.org> wrote:

> On Mon, Nov 2, 2020 at 9:12 AM Gustavo Pimentel
> <Gustavo.Pimentel@synopsys.com> wrote:
> >
> > On Mon, Nov 2, 2020 at 14:27:9, Vidya Sagar <vidyas@nvidia.com> wrote:
> >
> > >
> > >
> > > On 11/2/2020 7:45 PM, Rob Herring wrote:
> > > > External email: Use caution opening links or attachments
> > > >
> > > >
> > > > On Thu, Oct 29, 2020 at 12:40 AM Vidya Sagar <vidyas@nvidia.com> wrote:
> > > >>
> > > >> DesignWare core has a TLP digest (TD) override bit in one of the control
> > > >> registers of ATU. This bit also needs to be programmed for proper ECRC
> > > >> functionality. This is currently identified as an issue with DesignWare
> > > >> IP version 4.90a. This patch does the required programming in ATU upon
> > > >> querying the system policy for ECRC.
> > > >>
> > > >> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> > > >> Reviewed-by: Jingoo Han <jingoohan1@gmail.com>
> > > >> ---
> > > >> V3:
> > > >> * Added 'Reviewed-by: Jingoo Han <jingoohan1@gmail.com>'
> > > >>
> > > >> V2:
> > > >> * Addressed Jingoo's review comment
> > > >> * Removed saving 'td' bit information in 'dw_pcie' structure
> > > >>
> > > >>   drivers/pci/controller/dwc/pcie-designware.c | 8 ++++++--
> > > >>   drivers/pci/controller/dwc/pcie-designware.h | 1 +
> > > >>   2 files changed, 7 insertions(+), 2 deletions(-)
> > > >>
> > > >> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> > > >> index b5e438b70cd5..cbd651b219d2 100644
> > > >> --- a/drivers/pci/controller/dwc/pcie-designware.c
> > > >> +++ b/drivers/pci/controller/dwc/pcie-designware.c
> > > >> @@ -246,6 +246,8 @@ static void dw_pcie_prog_outbound_atu_unroll(struct dw_pcie *pci, u8 func_no,
> > > >>          dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_UPPER_TARGET,
> > > >>                                   upper_32_bits(pci_addr));
> > > >>          val = type | PCIE_ATU_FUNC_NUM(func_no);
> > > >> +       if (pci->version == 0x490A)
> > > >> +               val = val | pcie_is_ecrc_enabled() << PCIE_ATU_TD_SHIFT;
> > > >>          val = upper_32_bits(size - 1) ?
> > > >>                  val | PCIE_ATU_INCREASE_REGION_SIZE : val;
> > > >>          dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_REGION_CTRL1, val);
> > > >> @@ -294,8 +296,10 @@ static void __dw_pcie_prog_outbound_atu(struct dw_pcie *pci, u8 func_no,
> > > >>                             lower_32_bits(pci_addr));
> > > >>          dw_pcie_writel_dbi(pci, PCIE_ATU_UPPER_TARGET,
> > > >>                             upper_32_bits(pci_addr));
> > > >> -       dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, type |
> > > >> -                          PCIE_ATU_FUNC_NUM(func_no));
> > > >> +       val = type | PCIE_ATU_FUNC_NUM(func_no);
> > > >> +       if (pci->version == 0x490A)
> > > >
> > > > Is this even possible? Are the non-unroll ATU registers available post 4.80?
> > > I'm not sure. Gustavo might have information about this. I made this
> > > change so that it is taken care off even if they available.
> >
> > The Synopsys DesignWare PCIe IP is highly configurable, therefore is
> > dependable on what the design team has configured for their solution.
> > Although Synopsys doesn't recommend the use of non-unroll ATU, the
> > customers are free to select what they want for their design.
> 
> Okay, then there's a bug in the driver if the version is set to 0x480A
> or later and non-unroll is used:
> 
> if (pci->version >= 0x480A || (!pci->version &&
>        dw_pcie_iatu_unroll_enabled(pci))) {
> 
> Probably can just drop the version checking. The detection should always work.

Hi Rob,

The "detection" is based on the assumption that the read value on 
PCIE_ATU_VIEWPORT register is 0xffffffff (which is a hard-coded value by 
design), if it's true then the iATU is unrolled and the function returns 
1, otherwise is non-unrolled returns 0. So like you said it should always 
work, however, this code behavior was changed by Kishon on the following 
patch 2aadcb0cd39 ("PCI: dwc: Fix ATU identification for designware 
version >= 4.80"). His patch makes me believe that on keystone platform 
the read operation on that register causes some unpredicted behavior 
leads his platform to crash/abort, that's why he created this alternative 
version approach to avoid the "detection" algorithm.

From what I'm seeing the only drivers that use this "version" approach 
are the keystone and intel-gw (which probably doesn't need it).

To summarize, this is a workaround so that the keystone driver doesn't 
break independent of the controller IP version.

-Gustavo
> 
> Rob

Re: [PATCH V3 2/2] PCI: dwc: Add support to configure for ECRC

[Bjorn Helgaas]

On Thu, Oct 29, 2020 at 11:09:59AM +0530, Vidya Sagar wrote:
> DesignWare core has a TLP digest (TD) override bit in one of the control
> registers of ATU. This bit also needs to be programmed for proper ECRC
> functionality. This is currently identified as an issue with DesignWare
> IP version 4.90a. This patch does the required programming in ATU upon
> querying the system policy for ECRC.

I guess this is a hardware defect, right?

How much of a problem would it be if we instead added a "no_ecrc"
quirk for this hardware so we never enabled ECRC?

IIUC, the current Linux support of ECRC is a single choice at
boot-time: by default ECRC is not enabled, but if you boot with
"pci=ecrc=on", we turn on ECRC for every device.

That seems like the minimal support, but I think the spec allows ECRC
to be enabled selectively, on individual devices.  I can imagine a
sysfs knob that would allow us to enable/disable ECRC per-device at
run-time.

If we had such a sysfs knob, it would be pretty ugly and maybe
impractical to work around this hardware issue.  So I'm a little bit
hesitant to add functionality that might have to be removed in the
future.

> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> Reviewed-by: Jingoo Han <jingoohan1@gmail.com>
> ---
> V3:
> * Added 'Reviewed-by: Jingoo Han <jingoohan1@gmail.com>'
> 
> V2:
> * Addressed Jingoo's review comment
> * Removed saving 'td' bit information in 'dw_pcie' structure
> 
>  drivers/pci/controller/dwc/pcie-designware.c | 8 ++++++--
>  drivers/pci/controller/dwc/pcie-designware.h | 1 +
>  2 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> index b5e438b70cd5..cbd651b219d2 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.c
> +++ b/drivers/pci/controller/dwc/pcie-designware.c
> @@ -246,6 +246,8 @@ static void dw_pcie_prog_outbound_atu_unroll(struct dw_pcie *pci, u8 func_no,
>  	dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_UPPER_TARGET,
>  				 upper_32_bits(pci_addr));
>  	val = type | PCIE_ATU_FUNC_NUM(func_no);
> +	if (pci->version == 0x490A)
> +		val = val | pcie_is_ecrc_enabled() << PCIE_ATU_TD_SHIFT;
>  	val = upper_32_bits(size - 1) ?
>  		val | PCIE_ATU_INCREASE_REGION_SIZE : val;
>  	dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_REGION_CTRL1, val);
> @@ -294,8 +296,10 @@ static void __dw_pcie_prog_outbound_atu(struct dw_pcie *pci, u8 func_no,
>  			   lower_32_bits(pci_addr));
>  	dw_pcie_writel_dbi(pci, PCIE_ATU_UPPER_TARGET,
>  			   upper_32_bits(pci_addr));
> -	dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, type |
> -			   PCIE_ATU_FUNC_NUM(func_no));
> +	val = type | PCIE_ATU_FUNC_NUM(func_no);
> +	if (pci->version == 0x490A)
> +		val = val | pcie_is_ecrc_enabled() << PCIE_ATU_TD_SHIFT;
> +	dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, val);
>  	dw_pcie_writel_dbi(pci, PCIE_ATU_CR2, PCIE_ATU_ENABLE);
>  
>  	/*
> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> index e7f441441db2..b01ef407fd52 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.h
> +++ b/drivers/pci/controller/dwc/pcie-designware.h
> @@ -89,6 +89,7 @@
>  #define PCIE_ATU_TYPE_IO		0x2
>  #define PCIE_ATU_TYPE_CFG0		0x4
>  #define PCIE_ATU_TYPE_CFG1		0x5
> +#define PCIE_ATU_TD_SHIFT		8
>  #define PCIE_ATU_FUNC_NUM(pf)           ((pf) << 20)
>  #define PCIE_ATU_CR2			0x908
>  #define PCIE_ATU_ENABLE			BIT(31)
> -- 
> 2.17.1
> 

Re: [PATCH V3 2/2] PCI: dwc: Add support to configure for ECRC

[Vidya Sagar]

On 11/3/2020 4:32 AM, Bjorn Helgaas wrote:
> External email: Use caution opening links or attachments
> 
> 
> On Thu, Oct 29, 2020 at 11:09:59AM +0530, Vidya Sagar wrote:
>> DesignWare core has a TLP digest (TD) override bit in one of the control
>> registers of ATU. This bit also needs to be programmed for proper ECRC
>> functionality. This is currently identified as an issue with DesignWare
>> IP version 4.90a. This patch does the required programming in ATU upon
>> querying the system policy for ECRC.
> 
> I guess this is a hardware defect, right?
Yes. This is common across all DWC implementations (version 4.90 precisely)

> 
> How much of a problem would it be if we instead added a "no_ecrc"
> quirk for this hardware so we never enabled ECRC?
Well, on Tegra for some of the high fidelity use cases, ECRC is required 
to be turned on and if it can be done safely with these patches, why 
shouldn't we not enable ECRC at all?

> 
> IIUC, the current Linux support of ECRC is a single choice at
> boot-time: by default ECRC is not enabled, but if you boot with
> "pci=ecrc=on", we turn on ECRC for every device.
> 
> That seems like the minimal support, but I think the spec allows ECRC
> to be enabled selectively, on individual devices.  I can imagine a
> sysfs knob that would allow us to enable/disable ECRC per-device at
> run-time.
> 
> If we had such a sysfs knob, it would be pretty ugly and maybe
> impractical to work around this hardware issue.  So I'm a little bit
> hesitant to add functionality that might have to be removed in the
> future.
Agree with this. But since it is a boot-time choice at this point, I 
think we can still go ahead with this approach to have a working ECRC 
mechanism right? I don't see any sysfs knob for AER controlling at this 
point.

> 
>> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
>> Reviewed-by: Jingoo Han <jingoohan1@gmail.com>
>> ---
>> V3:
>> * Added 'Reviewed-by: Jingoo Han <jingoohan1@gmail.com>'
>>
>> V2:
>> * Addressed Jingoo's review comment
>> * Removed saving 'td' bit information in 'dw_pcie' structure
>>
>>   drivers/pci/controller/dwc/pcie-designware.c | 8 ++++++--
>>   drivers/pci/controller/dwc/pcie-designware.h | 1 +
>>   2 files changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
>> index b5e438b70cd5..cbd651b219d2 100644
>> --- a/drivers/pci/controller/dwc/pcie-designware.c
>> +++ b/drivers/pci/controller/dwc/pcie-designware.c
>> @@ -246,6 +246,8 @@ static void dw_pcie_prog_outbound_atu_unroll(struct dw_pcie *pci, u8 func_no,
>>        dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_UPPER_TARGET,
>>                                 upper_32_bits(pci_addr));
>>        val = type | PCIE_ATU_FUNC_NUM(func_no);
>> +     if (pci->version == 0x490A)
>> +             val = val | pcie_is_ecrc_enabled() << PCIE_ATU_TD_SHIFT;
>>        val = upper_32_bits(size - 1) ?
>>                val | PCIE_ATU_INCREASE_REGION_SIZE : val;
>>        dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_REGION_CTRL1, val);
>> @@ -294,8 +296,10 @@ static void __dw_pcie_prog_outbound_atu(struct dw_pcie *pci, u8 func_no,
>>                           lower_32_bits(pci_addr));
>>        dw_pcie_writel_dbi(pci, PCIE_ATU_UPPER_TARGET,
>>                           upper_32_bits(pci_addr));
>> -     dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, type |
>> -                        PCIE_ATU_FUNC_NUM(func_no));
>> +     val = type | PCIE_ATU_FUNC_NUM(func_no);
>> +     if (pci->version == 0x490A)
>> +             val = val | pcie_is_ecrc_enabled() << PCIE_ATU_TD_SHIFT;
>> +     dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, val);
>>        dw_pcie_writel_dbi(pci, PCIE_ATU_CR2, PCIE_ATU_ENABLE);
>>
>>        /*
>> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
>> index e7f441441db2..b01ef407fd52 100644
>> --- a/drivers/pci/controller/dwc/pcie-designware.h
>> +++ b/drivers/pci/controller/dwc/pcie-designware.h
>> @@ -89,6 +89,7 @@
>>   #define PCIE_ATU_TYPE_IO             0x2
>>   #define PCIE_ATU_TYPE_CFG0           0x4
>>   #define PCIE_ATU_TYPE_CFG1           0x5
>> +#define PCIE_ATU_TD_SHIFT            8
>>   #define PCIE_ATU_FUNC_NUM(pf)           ((pf) << 20)
>>   #define PCIE_ATU_CR2                 0x908
>>   #define PCIE_ATU_ENABLE                      BIT(31)
>> --
>> 2.17.1
>>

Re: [PATCH V3 2/2] PCI: dwc: Add support to configure for ECRC

[Rob Herring]

On Mon, Nov 2, 2020 at 4:38 PM Gustavo Pimentel
<Gustavo.Pimentel@synopsys.com> wrote:
>
> On Mon, Nov 2, 2020 at 21:16:52, Rob Herring <robh@kernel.org> wrote:
>
> > On Mon, Nov 2, 2020 at 9:12 AM Gustavo Pimentel
> > <Gustavo.Pimentel@synopsys.com> wrote:
> > >
> > > On Mon, Nov 2, 2020 at 14:27:9, Vidya Sagar <vidyas@nvidia.com> wrote:
> > >
> > > >
> > > >
> > > > On 11/2/2020 7:45 PM, Rob Herring wrote:
> > > > > External email: Use caution opening links or attachments
> > > > >
> > > > >
> > > > > On Thu, Oct 29, 2020 at 12:40 AM Vidya Sagar <vidyas@nvidia.com> wrote:
> > > > >>
> > > > >> DesignWare core has a TLP digest (TD) override bit in one of the control
> > > > >> registers of ATU. This bit also needs to be programmed for proper ECRC
> > > > >> functionality. This is currently identified as an issue with DesignWare
> > > > >> IP version 4.90a. This patch does the required programming in ATU upon
> > > > >> querying the system policy for ECRC.
> > > > >>
> > > > >> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> > > > >> Reviewed-by: Jingoo Han <jingoohan1@gmail.com>
> > > > >> ---
> > > > >> V3:
> > > > >> * Added 'Reviewed-by: Jingoo Han <jingoohan1@gmail.com>'
> > > > >>
> > > > >> V2:
> > > > >> * Addressed Jingoo's review comment
> > > > >> * Removed saving 'td' bit information in 'dw_pcie' structure
> > > > >>
> > > > >>   drivers/pci/controller/dwc/pcie-designware.c | 8 ++++++--
> > > > >>   drivers/pci/controller/dwc/pcie-designware.h | 1 +
> > > > >>   2 files changed, 7 insertions(+), 2 deletions(-)
> > > > >>
> > > > >> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> > > > >> index b5e438b70cd5..cbd651b219d2 100644
> > > > >> --- a/drivers/pci/controller/dwc/pcie-designware.c
> > > > >> +++ b/drivers/pci/controller/dwc/pcie-designware.c
> > > > >> @@ -246,6 +246,8 @@ static void dw_pcie_prog_outbound_atu_unroll(struct dw_pcie *pci, u8 func_no,
> > > > >>          dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_UPPER_TARGET,
> > > > >>                                   upper_32_bits(pci_addr));
> > > > >>          val = type | PCIE_ATU_FUNC_NUM(func_no);
> > > > >> +       if (pci->version == 0x490A)
> > > > >> +               val = val | pcie_is_ecrc_enabled() << PCIE_ATU_TD_SHIFT;
> > > > >>          val = upper_32_bits(size - 1) ?
> > > > >>                  val | PCIE_ATU_INCREASE_REGION_SIZE : val;
> > > > >>          dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_REGION_CTRL1, val);
> > > > >> @@ -294,8 +296,10 @@ static void __dw_pcie_prog_outbound_atu(struct dw_pcie *pci, u8 func_no,
> > > > >>                             lower_32_bits(pci_addr));
> > > > >>          dw_pcie_writel_dbi(pci, PCIE_ATU_UPPER_TARGET,
> > > > >>                             upper_32_bits(pci_addr));
> > > > >> -       dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, type |
> > > > >> -                          PCIE_ATU_FUNC_NUM(func_no));
> > > > >> +       val = type | PCIE_ATU_FUNC_NUM(func_no);
> > > > >> +       if (pci->version == 0x490A)
> > > > >
> > > > > Is this even possible? Are the non-unroll ATU registers available post 4.80?
> > > > I'm not sure. Gustavo might have information about this. I made this
> > > > change so that it is taken care off even if they available.
> > >
> > > The Synopsys DesignWare PCIe IP is highly configurable, therefore is
> > > dependable on what the design team has configured for their solution.
> > > Although Synopsys doesn't recommend the use of non-unroll ATU, the
> > > customers are free to select what they want for their design.

Then given the feature is not really tied to the IP version, using
version wasn't really a good choice. A better choice would have been a
quirk flag that platforms could set. Perhaps called
'iatu_unroll_enabled'...

> > Okay, then there's a bug in the driver if the version is set to 0x480A
> > or later and non-unroll is used:
> >
> > if (pci->version >= 0x480A || (!pci->version &&
> >        dw_pcie_iatu_unroll_enabled(pci))) {
> >
> > Probably can just drop the version checking. The detection should always work.
>
> Hi Rob,
>
> The "detection" is based on the assumption that the read value on
> PCIE_ATU_VIEWPORT register is 0xffffffff (which is a hard-coded value by
> design), if it's true then the iATU is unrolled and the function returns
> 1, otherwise is non-unrolled returns 0. So like you said it should always
> work, however, this code behavior was changed by Kishon on the following
> patch 2aadcb0cd39 ("PCI: dwc: Fix ATU identification for designware
> version >= 4.80"). His patch makes me believe that on keystone platform
> the read operation on that register causes some unpredicted behavior
> leads his platform to crash/abort, that's why he created this alternative
> version approach to avoid the "detection" algorithm.

Ah, h/w designers and their love for bus aborts...

> From what I'm seeing the only drivers that use this "version" approach
> are the keystone and intel-gw (which probably doesn't need it).
>
> To summarize, this is a workaround so that the keystone driver doesn't
> break independent of the controller IP version.

Keystone is also broken in another way. The dts files claim 16 in and
out regions, but the ATU region is 4KB. It would need 8KB for 16
regions as unroll has a stride of 512bytes for each region.

Rob

Re: [PATCH V3 2/2] PCI: dwc: Add support to configure for ECRC

[Bjorn Helgaas]

On Tue, Nov 03, 2020 at 08:57:01AM +0530, Vidya Sagar wrote:
> On 11/3/2020 4:32 AM, Bjorn Helgaas wrote:
> > On Thu, Oct 29, 2020 at 11:09:59AM +0530, Vidya Sagar wrote:
> > > DesignWare core has a TLP digest (TD) override bit in one of the control
> > > registers of ATU. This bit also needs to be programmed for proper ECRC
> > > functionality. This is currently identified as an issue with DesignWare
> > > IP version 4.90a. This patch does the required programming in ATU upon
> > > querying the system policy for ECRC.
> > 
> > I guess this is a hardware defect, right?
> Yes. This is common across all DWC implementations (version 4.90 precisely)
> 
> > How much of a problem would it be if we instead added a "no_ecrc"
> > quirk for this hardware so we never enabled ECRC?
> Well, on Tegra for some of the high fidelity use cases, ECRC is required to
> be turned on and if it can be done safely with these patches, why shouldn't
> we not enable ECRC at all?
> 
> > IIUC, the current Linux support of ECRC is a single choice at
> > boot-time: by default ECRC is not enabled, but if you boot with
> > "pci=ecrc=on", we turn on ECRC for every device.
> > 
> > That seems like the minimal support, but I think the spec allows ECRC
> > to be enabled selectively, on individual devices.  I can imagine a
> > sysfs knob that would allow us to enable/disable ECRC per-device at
> > run-time.
> > 
> > If we had such a sysfs knob, it would be pretty ugly and maybe
> > impractical to work around this hardware issue.  So I'm a little bit
> > hesitant to add functionality that might have to be removed in the
> > future.
>
> Agree with this. But since it is a boot-time choice at this point, I think
> we can still go ahead with this approach to have a working ECRC mechanism
> right? I don't see any sysfs knob for AER controlling at this point.

I don't want to do anything that will prevent us from adding
per-device ECRC control in the future.

My concern is that if we add a run-time sysfs knob in the future, the
user experience on this hardware will be poor because there's no
convenient path to twiddle the PCIE_ATU_TD bit when the generic code
changes the AER Control bit.

What is the failure mode in these scenarios:

  - User boots with defaults, ECRC is disabled.
  - User enables ECRC via sysfs.
  - What happens here?  ECRC is enabled via AER Control but not via
    DWC TD bit.  I assume ECRC doesn't work.  Does it cause PCIe
    errors (malformed TLP, etc)?

Or this one:

  - User boots with "pci=ecrc=on", ECRC is enabled.
  - ECRC works fine.
  - User disables ECRC via sysfs.
  - What happens here?  ECRC is disabled via AER Control, but DWC TD
    bit thinks it's still enabled.

If you enabled ECRC unconditionally on DWC and the sysfs knob had no
effect, I'd be OK with that.  I'm more worried about what happens when
the AER bit and the DWC TD bit are set so they don't match.  What is
the failure mode there?

> > > Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> > > Reviewed-by: Jingoo Han <jingoohan1@gmail.com>
> > > ---
> > > V3:
> > > * Added 'Reviewed-by: Jingoo Han <jingoohan1@gmail.com>'
> > > 
> > > V2:
> > > * Addressed Jingoo's review comment
> > > * Removed saving 'td' bit information in 'dw_pcie' structure
> > > 
> > >   drivers/pci/controller/dwc/pcie-designware.c | 8 ++++++--
> > >   drivers/pci/controller/dwc/pcie-designware.h | 1 +
> > >   2 files changed, 7 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> > > index b5e438b70cd5..cbd651b219d2 100644
> > > --- a/drivers/pci/controller/dwc/pcie-designware.c
> > > +++ b/drivers/pci/controller/dwc/pcie-designware.c
> > > @@ -246,6 +246,8 @@ static void dw_pcie_prog_outbound_atu_unroll(struct dw_pcie *pci, u8 func_no,
> > >        dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_UPPER_TARGET,
> > >                                 upper_32_bits(pci_addr));
> > >        val = type | PCIE_ATU_FUNC_NUM(func_no);
> > > +     if (pci->version == 0x490A)
> > > +             val = val | pcie_is_ecrc_enabled() << PCIE_ATU_TD_SHIFT;
> > >        val = upper_32_bits(size - 1) ?
> > >                val | PCIE_ATU_INCREASE_REGION_SIZE : val;
> > >        dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_REGION_CTRL1, val);
> > > @@ -294,8 +296,10 @@ static void __dw_pcie_prog_outbound_atu(struct dw_pcie *pci, u8 func_no,
> > >                           lower_32_bits(pci_addr));
> > >        dw_pcie_writel_dbi(pci, PCIE_ATU_UPPER_TARGET,
> > >                           upper_32_bits(pci_addr));
> > > -     dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, type |
> > > -                        PCIE_ATU_FUNC_NUM(func_no));
> > > +     val = type | PCIE_ATU_FUNC_NUM(func_no);
> > > +     if (pci->version == 0x490A)
> > > +             val = val | pcie_is_ecrc_enabled() << PCIE_ATU_TD_SHIFT;
> > > +     dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, val);
> > >        dw_pcie_writel_dbi(pci, PCIE_ATU_CR2, PCIE_ATU_ENABLE);
> > > 
> > >        /*
> > > diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> > > index e7f441441db2..b01ef407fd52 100644
> > > --- a/drivers/pci/controller/dwc/pcie-designware.h
> > > +++ b/drivers/pci/controller/dwc/pcie-designware.h
> > > @@ -89,6 +89,7 @@
> > >   #define PCIE_ATU_TYPE_IO             0x2
> > >   #define PCIE_ATU_TYPE_CFG0           0x4
> > >   #define PCIE_ATU_TYPE_CFG1           0x5
> > > +#define PCIE_ATU_TD_SHIFT            8
> > >   #define PCIE_ATU_FUNC_NUM(pf)           ((pf) << 20)
> > >   #define PCIE_ATU_CR2                 0x908
> > >   #define PCIE_ATU_ENABLE                      BIT(31)
> > > --
> > > 2.17.1
> > > 

Re: [PATCH V3 2/2] PCI: dwc: Add support to configure for ECRC

[Vidya Sagar]

On 11/4/2020 2:37 AM, Bjorn Helgaas wrote:
> External email: Use caution opening links or attachments
> 
> 
> On Tue, Nov 03, 2020 at 08:57:01AM +0530, Vidya Sagar wrote:
>> On 11/3/2020 4:32 AM, Bjorn Helgaas wrote:
>>> On Thu, Oct 29, 2020 at 11:09:59AM +0530, Vidya Sagar wrote:
>>>> DesignWare core has a TLP digest (TD) override bit in one of the control
>>>> registers of ATU. This bit also needs to be programmed for proper ECRC
>>>> functionality. This is currently identified as an issue with DesignWare
>>>> IP version 4.90a. This patch does the required programming in ATU upon
>>>> querying the system policy for ECRC.
>>>
>>> I guess this is a hardware defect, right?
>> Yes. This is common across all DWC implementations (version 4.90 precisely)
>>
>>> How much of a problem would it be if we instead added a "no_ecrc"
>>> quirk for this hardware so we never enabled ECRC?
>> Well, on Tegra for some of the high fidelity use cases, ECRC is required to
>> be turned on and if it can be done safely with these patches, why shouldn't
>> we not enable ECRC at all?
>>
>>> IIUC, the current Linux support of ECRC is a single choice at
>>> boot-time: by default ECRC is not enabled, but if you boot with
>>> "pci=ecrc=on", we turn on ECRC for every device.
>>>
>>> That seems like the minimal support, but I think the spec allows ECRC
>>> to be enabled selectively, on individual devices.  I can imagine a
>>> sysfs knob that would allow us to enable/disable ECRC per-device at
>>> run-time.
>>>
>>> If we had such a sysfs knob, it would be pretty ugly and maybe
>>> impractical to work around this hardware issue.  So I'm a little bit
>>> hesitant to add functionality that might have to be removed in the
>>> future.
>>
>> Agree with this. But since it is a boot-time choice at this point, I think
>> we can still go ahead with this approach to have a working ECRC mechanism
>> right? I don't see any sysfs knob for AER controlling at this point.
> 
> I don't want to do anything that will prevent us from adding
> per-device ECRC control in the future.
> 
> My concern is that if we add a run-time sysfs knob in the future, the
> user experience on this hardware will be poor because there's no
> convenient path to twiddle the PCIE_ATU_TD bit when the generic code
> changes the AER Control bit.
Agree.
Can we add it to the documentation that run time changing of ECRC 
settings are not supported on this (i.e. Tegra194) platform (or for that 
matter on any SoC with PCIe based on DesignWare core version 4.90A). By 
'not supported', I meant that the ECRC digest part may not work but the 
normal functionality will continue to work without reporting any AER 
errors. I tried to emulate the following scenarios on Tegra194 silicon 
and here are my observations.
FWIW, I'm referring to the PCIe spec Rev 5.0 Ver 1.0 (22 May 2019)

> 
> What is the failure mode in these scenarios:
> 
>    - User boots with defaults, ECRC is disabled.
>    - User enables ECRC via sysfs.
>    - What happens here?  ECRC is enabled via AER Control but not via
>      DWC TD bit.  I assume ECRC doesn't work.  Does it cause PCIe
>      errors (malformed TLP, etc)?
Since DWC TD bit is not programmed, for all the transactions that go 
through ATU, TLP Digest won't get generated (although AER registers 
indicate that ECRC should get generated).
As per the spec section "2.7.1 ECRC Rules"

---
If a device Function is enabled to generate ECRC, it must calculate and 
apply ECRC for all TLPs originated by the Function
---

So the RP would be violating the PCIe spec, but it doesn't result in any 
error because the same section has the following rule as well

---
If a device Function is enabled to check ECRC, it must do so for all 
TLPs with ECRC where the device is the ultimate PCI Express Receiver
	Note that it is still possible for the Function to receive TLPs without 
ECRC, and these are processed normally - this is not an error
---

so, even if the EP has ECRC check enabled, because of the above rule, it 
just processes those packets without ECRC as normal packets.
Basically, whoever is enabling ECRC run time gets cheated as 
transactions routed through ATU don't really have ECRC digest

> 
> Or this one:
> 
>    - User boots with "pci=ecrc=on", ECRC is enabled.
>    - ECRC works fine.
>    - User disables ECRC via sysfs.
>    - What happens here?  ECRC is disabled via AER Control, but DWC TD
>      bit thinks it's still enabled.
In this case, the EP doesn't have ECRC check enabled but receives TLPs 
with ECRC digest. This again won't result in any error because of the 
section "2.2.3 TLP Digest Rules" which says

---
If an intermediate or ultimate PCI Express Receiver of the TLP does not 
support ECRC checking, the Receiver must ignore the TLP Digest
---

So the EP just ignores the TLP Digest and process the TLP normally.
Although functionality wise there is no issue here, there could be some 
impact on the perf because of the extra DWord data. This is again 
debatable as the perf/data path is typically from EP's DMA engine to 
host system memory and not config/BAR accesses.
> 
> If you enabled ECRC unconditionally on DWC and the sysfs knob had no
> effect, I'd be OK with that.  I'm more worried about what happens when
> the AER bit and the DWC TD bit are set so they don't match.  What is
> the failure mode there?
Based on the above experiments, we can as well keep the DWC TD bit 
programmed unconditionally and it won't lead to any errors. As mentioned 
before, the only downside of it is the extra DWord in each ATU routed 
TLP which may load the bus (in downstream direction) with no real 
benefit as such.

Please let me know where can we go from here.
I can push a different patch to keep DWC TD bit always programmed if 
that is the best approach to take at this point.
> 
>>>> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
>>>> Reviewed-by: Jingoo Han <jingoohan1@gmail.com>
>>>> ---
>>>> V3:
>>>> * Added 'Reviewed-by: Jingoo Han <jingoohan1@gmail.com>'
>>>>
>>>> V2:
>>>> * Addressed Jingoo's review comment
>>>> * Removed saving 'td' bit information in 'dw_pcie' structure
>>>>
>>>>    drivers/pci/controller/dwc/pcie-designware.c | 8 ++++++--
>>>>    drivers/pci/controller/dwc/pcie-designware.h | 1 +
>>>>    2 files changed, 7 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
>>>> index b5e438b70cd5..cbd651b219d2 100644
>>>> --- a/drivers/pci/controller/dwc/pcie-designware.c
>>>> +++ b/drivers/pci/controller/dwc/pcie-designware.c
>>>> @@ -246,6 +246,8 @@ static void dw_pcie_prog_outbound_atu_unroll(struct dw_pcie *pci, u8 func_no,
>>>>         dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_UPPER_TARGET,
>>>>                                  upper_32_bits(pci_addr));
>>>>         val = type | PCIE_ATU_FUNC_NUM(func_no);
>>>> +     if (pci->version == 0x490A)
>>>> +             val = val | pcie_is_ecrc_enabled() << PCIE_ATU_TD_SHIFT;
>>>>         val = upper_32_bits(size - 1) ?
>>>>                 val | PCIE_ATU_INCREASE_REGION_SIZE : val;
>>>>         dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_REGION_CTRL1, val);
>>>> @@ -294,8 +296,10 @@ static void __dw_pcie_prog_outbound_atu(struct dw_pcie *pci, u8 func_no,
>>>>                            lower_32_bits(pci_addr));
>>>>         dw_pcie_writel_dbi(pci, PCIE_ATU_UPPER_TARGET,
>>>>                            upper_32_bits(pci_addr));
>>>> -     dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, type |
>>>> -                        PCIE_ATU_FUNC_NUM(func_no));
>>>> +     val = type | PCIE_ATU_FUNC_NUM(func_no);
>>>> +     if (pci->version == 0x490A)
>>>> +             val = val | pcie_is_ecrc_enabled() << PCIE_ATU_TD_SHIFT;
>>>> +     dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, val);
>>>>         dw_pcie_writel_dbi(pci, PCIE_ATU_CR2, PCIE_ATU_ENABLE);
>>>>
>>>>         /*
>>>> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
>>>> index e7f441441db2..b01ef407fd52 100644
>>>> --- a/drivers/pci/controller/dwc/pcie-designware.h
>>>> +++ b/drivers/pci/controller/dwc/pcie-designware.h
>>>> @@ -89,6 +89,7 @@
>>>>    #define PCIE_ATU_TYPE_IO             0x2
>>>>    #define PCIE_ATU_TYPE_CFG0           0x4
>>>>    #define PCIE_ATU_TYPE_CFG1           0x5
>>>> +#define PCIE_ATU_TD_SHIFT            8
>>>>    #define PCIE_ATU_FUNC_NUM(pf)           ((pf) << 20)
>>>>    #define PCIE_ATU_CR2                 0x908
>>>>    #define PCIE_ATU_ENABLE                      BIT(31)
>>>> --
>>>> 2.17.1
>>>>

Re: [PATCH V3 2/2] PCI: dwc: Add support to configure for ECRC

[Bjorn Helgaas]

On Wed, Nov 04, 2020 at 05:13:07PM +0530, Vidya Sagar wrote:
> On 11/4/2020 2:37 AM, Bjorn Helgaas wrote:
> > On Tue, Nov 03, 2020 at 08:57:01AM +0530, Vidya Sagar wrote:
> > > On 11/3/2020 4:32 AM, Bjorn Helgaas wrote:
> > > > On Thu, Oct 29, 2020 at 11:09:59AM +0530, Vidya Sagar wrote:
> > > > > DesignWare core has a TLP digest (TD) override bit in one of the control
> > > > > registers of ATU. This bit also needs to be programmed for proper ECRC
> > > > > functionality. This is currently identified as an issue with DesignWare
> > > > > IP version 4.90a. This patch does the required programming in ATU upon
> > > > > querying the system policy for ECRC.
> > > > 
> > > > I guess this is a hardware defect, right?
> > > Yes. This is common across all DWC implementations (version 4.90 precisely)
> > > 
> > > > How much of a problem would it be if we instead added a "no_ecrc"
> > > > quirk for this hardware so we never enabled ECRC?
> > > Well, on Tegra for some of the high fidelity use cases, ECRC is required to
> > > be turned on and if it can be done safely with these patches, why shouldn't
> > > we not enable ECRC at all?
> > > 
> > > > IIUC, the current Linux support of ECRC is a single choice at
> > > > boot-time: by default ECRC is not enabled, but if you boot with
> > > > "pci=ecrc=on", we turn on ECRC for every device.
> > > > 
> > > > That seems like the minimal support, but I think the spec allows ECRC
> > > > to be enabled selectively, on individual devices.  I can imagine a
> > > > sysfs knob that would allow us to enable/disable ECRC per-device at
> > > > run-time.
> > > > 
> > > > If we had such a sysfs knob, it would be pretty ugly and maybe
> > > > impractical to work around this hardware issue.  So I'm a little bit
> > > > hesitant to add functionality that might have to be removed in the
> > > > future.
> > > 
> > > Agree with this. But since it is a boot-time choice at this point, I think
> > > we can still go ahead with this approach to have a working ECRC mechanism
> > > right? I don't see any sysfs knob for AER controlling at this point.
> > 
> > I don't want to do anything that will prevent us from adding
> > per-device ECRC control in the future.
> > 
> > My concern is that if we add a run-time sysfs knob in the future, the
> > user experience on this hardware will be poor because there's no
> > convenient path to twiddle the PCIE_ATU_TD bit when the generic code
> > changes the AER Control bit.
>
> Agree.
> Can we add it to the documentation that run time changing of ECRC settings
> are not supported on this (i.e. Tegra194) platform (or for that matter on
> any SoC with PCIe based on DesignWare core version 4.90A). By 'not
> supported', I meant that the ECRC digest part may not work but the normal
> functionality will continue to work without reporting any AER errors. I
> tried to emulate the following scenarios on Tegra194 silicon and here are my
> observations.
> FWIW, I'm referring to the PCIe spec Rev 5.0 Ver 1.0 (22 May 2019)
> 
> > What is the failure mode in these scenarios:
> > 
> >    - User boots with defaults, ECRC is disabled.
> >    - User enables ECRC via sysfs.
> >    - What happens here?  ECRC is enabled via AER Control but not via
> >      DWC TD bit.  I assume ECRC doesn't work.  Does it cause PCIe
> >      errors (malformed TLP, etc)?
>
> Since DWC TD bit is not programmed, for all the transactions that go through
> ATU, TLP Digest won't get generated (although AER registers indicate that
> ECRC should get generated).
> As per the spec section "2.7.1 ECRC Rules"
> 
> ---
> If a device Function is enabled to generate ECRC, it must calculate and
> apply ECRC for all TLPs originated by the Function
> ---
> 
> So the RP would be violating the PCIe spec, but it doesn't result in any
> error because the same section has the following rule as well
> 
> ---
> If a device Function is enabled to check ECRC, it must do so for all TLPs
> with ECRC where the device is the ultimate PCI Express Receiver
> 	Note that it is still possible for the Function to receive TLPs without
> ECRC, and these are processed normally - this is not an error
> ---
> 
> so, even if the EP has ECRC check enabled, because of the above rule, it
> just processes those packets without ECRC as normal packets.
> Basically, whoever is enabling ECRC run time gets cheated as transactions
> routed through ATU don't really have ECRC digest
> 
> > Or this one:
> > 
> >    - User boots with "pci=ecrc=on", ECRC is enabled.
> >    - ECRC works fine.
> >    - User disables ECRC via sysfs.
> >    - What happens here?  ECRC is disabled via AER Control, but DWC TD
> >      bit thinks it's still enabled.
>
> In this case, the EP doesn't have ECRC check enabled but receives TLPs with
> ECRC digest. This again won't result in any error because of the section
> "2.2.3 TLP Digest Rules" which says
> 
> ---
> If an intermediate or ultimate PCI Express Receiver of the TLP does not
> support ECRC checking, the Receiver must ignore the TLP Digest
> ---
> 
> So the EP just ignores the TLP Digest and process the TLP normally.
> Although functionality wise there is no issue here, there could be some
> impact on the perf because of the extra DWord data. This is again debatable
> as the perf/data path is typically from EP's DMA engine to host system
> memory and not config/BAR accesses.
> > 
> > If you enabled ECRC unconditionally on DWC and the sysfs knob had no
> > effect, I'd be OK with that.  I'm more worried about what happens when
> > the AER bit and the DWC TD bit are set so they don't match.  What is
> > the failure mode there?
>
> Based on the above experiments, we can as well keep the DWC TD bit
> programmed unconditionally and it won't lead to any errors. As mentioned
> before, the only downside of it is the extra DWord in each ATU routed TLP
> which may load the bus (in downstream direction) with no real benefit as
> such.

IIUC the issue only affects traffic from the Root Port to the
Endpoint, and traffic going upstream is unaffected.  Here's what I
think happens based on the RP and EP settings, please correct me if
wrong:

  1)  RP TD+ ECRC_gen+       generates ECRC
      EP     ECRC_check-     ignores ECRC
      EP     ECRC_check+     checks ECRC

  2)  RP TD+ ECRC_gen-       generates ECRC when it shouldn't (defect)
      EP     ECRC_check-     ignores ECRC
      EP     ECRC_check+     checks ECRC (may signal errors)

  3)  RP TD- ECRC_gen+       fails to generate ECRC (defect)
      EP     ECRC_check-     ignores ECRC
      EP     ECRC_check+     handles TLPs without ECRC normally,
                             but cannot detect ECRC errors

  4)  RP TD- ECRC_gen-       no ECRC generated (as expected)
      EP     ECRC_check-     ignores ECRC
      EP     ECRC_check+     handles TLPs without ECRC normally

If my assumptions above are correct, this defect never causes extra
errors like Malformed TLP, etc, to be signaled regardless of the AER
ECRC_check settings.

The only functional problem is that in case 3, the EP *should* be able
to check and signal ECRC errors, but it cannot because the RP doesn't
generate ECRC.

Case 2 is a performance issue because we add the extra dword in every
TLP going downstream.  That doesn't seem unreasonable since this is
just config and BAR accesses.  The EP may detect ECRC errors when we
don't think the RP is even generating ECRC, but in general we won't
enable checking in the EP unless we also enable generation in the RP.

So I think setting the DWC TD bit unconditionally seems like a pretty
good solution.

> Please let me know where can we go from here.
> I can push a different patch to keep DWC TD bit always programmed if that is
> the best approach to take at this point.
> > 
> > > > > Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> > > > > Reviewed-by: Jingoo Han <jingoohan1@gmail.com>
> > > > > ---
> > > > > V3:
> > > > > * Added 'Reviewed-by: Jingoo Han <jingoohan1@gmail.com>'
> > > > > 
> > > > > V2:
> > > > > * Addressed Jingoo's review comment
> > > > > * Removed saving 'td' bit information in 'dw_pcie' structure
> > > > > 
> > > > >    drivers/pci/controller/dwc/pcie-designware.c | 8 ++++++--
> > > > >    drivers/pci/controller/dwc/pcie-designware.h | 1 +
> > > > >    2 files changed, 7 insertions(+), 2 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> > > > > index b5e438b70cd5..cbd651b219d2 100644
> > > > > --- a/drivers/pci/controller/dwc/pcie-designware.c
> > > > > +++ b/drivers/pci/controller/dwc/pcie-designware.c
> > > > > @@ -246,6 +246,8 @@ static void dw_pcie_prog_outbound_atu_unroll(struct dw_pcie *pci, u8 func_no,
> > > > >         dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_UPPER_TARGET,
> > > > >                                  upper_32_bits(pci_addr));
> > > > >         val = type | PCIE_ATU_FUNC_NUM(func_no);
> > > > > +     if (pci->version == 0x490A)
> > > > > +             val = val | pcie_is_ecrc_enabled() << PCIE_ATU_TD_SHIFT;
> > > > >         val = upper_32_bits(size - 1) ?
> > > > >                 val | PCIE_ATU_INCREASE_REGION_SIZE : val;
> > > > >         dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_REGION_CTRL1, val);
> > > > > @@ -294,8 +296,10 @@ static void __dw_pcie_prog_outbound_atu(struct dw_pcie *pci, u8 func_no,
> > > > >                            lower_32_bits(pci_addr));
> > > > >         dw_pcie_writel_dbi(pci, PCIE_ATU_UPPER_TARGET,
> > > > >                            upper_32_bits(pci_addr));
> > > > > -     dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, type |
> > > > > -                        PCIE_ATU_FUNC_NUM(func_no));
> > > > > +     val = type | PCIE_ATU_FUNC_NUM(func_no);
> > > > > +     if (pci->version == 0x490A)
> > > > > +             val = val | pcie_is_ecrc_enabled() << PCIE_ATU_TD_SHIFT;
> > > > > +     dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, val);
> > > > >         dw_pcie_writel_dbi(pci, PCIE_ATU_CR2, PCIE_ATU_ENABLE);
> > > > > 
> > > > >         /*
> > > > > diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> > > > > index e7f441441db2..b01ef407fd52 100644
> > > > > --- a/drivers/pci/controller/dwc/pcie-designware.h
> > > > > +++ b/drivers/pci/controller/dwc/pcie-designware.h
> > > > > @@ -89,6 +89,7 @@
> > > > >    #define PCIE_ATU_TYPE_IO             0x2
> > > > >    #define PCIE_ATU_TYPE_CFG0           0x4
> > > > >    #define PCIE_ATU_TYPE_CFG1           0x5
> > > > > +#define PCIE_ATU_TD_SHIFT            8
> > > > >    #define PCIE_ATU_FUNC_NUM(pf)           ((pf) << 20)
> > > > >    #define PCIE_ATU_CR2                 0x908
> > > > >    #define PCIE_ATU_ENABLE                      BIT(31)
> > > > > --
> > > > > 2.17.1
> > > > > 

Re: [PATCH V3 2/2] PCI: dwc: Add support to configure for ECRC

[Vidya Sagar]

On 11/4/2020 9:52 PM, Bjorn Helgaas wrote:
> External email: Use caution opening links or attachments
> 
> 
> On Wed, Nov 04, 2020 at 05:13:07PM +0530, Vidya Sagar wrote:
>> On 11/4/2020 2:37 AM, Bjorn Helgaas wrote:
>>> On Tue, Nov 03, 2020 at 08:57:01AM +0530, Vidya Sagar wrote:
>>>> On 11/3/2020 4:32 AM, Bjorn Helgaas wrote:
>>>>> On Thu, Oct 29, 2020 at 11:09:59AM +0530, Vidya Sagar wrote:
>>>>>> DesignWare core has a TLP digest (TD) override bit in one of the control
>>>>>> registers of ATU. This bit also needs to be programmed for proper ECRC
>>>>>> functionality. This is currently identified as an issue with DesignWare
>>>>>> IP version 4.90a. This patch does the required programming in ATU upon
>>>>>> querying the system policy for ECRC.
>>>>>
>>>>> I guess this is a hardware defect, right?
>>>> Yes. This is common across all DWC implementations (version 4.90 precisely)
>>>>
>>>>> How much of a problem would it be if we instead added a "no_ecrc"
>>>>> quirk for this hardware so we never enabled ECRC?
>>>> Well, on Tegra for some of the high fidelity use cases, ECRC is required to
>>>> be turned on and if it can be done safely with these patches, why shouldn't
>>>> we not enable ECRC at all?
>>>>
>>>>> IIUC, the current Linux support of ECRC is a single choice at
>>>>> boot-time: by default ECRC is not enabled, but if you boot with
>>>>> "pci=ecrc=on", we turn on ECRC for every device.
>>>>>
>>>>> That seems like the minimal support, but I think the spec allows ECRC
>>>>> to be enabled selectively, on individual devices.  I can imagine a
>>>>> sysfs knob that would allow us to enable/disable ECRC per-device at
>>>>> run-time.
>>>>>
>>>>> If we had such a sysfs knob, it would be pretty ugly and maybe
>>>>> impractical to work around this hardware issue.  So I'm a little bit
>>>>> hesitant to add functionality that might have to be removed in the
>>>>> future.
>>>>
>>>> Agree with this. But since it is a boot-time choice at this point, I think
>>>> we can still go ahead with this approach to have a working ECRC mechanism
>>>> right? I don't see any sysfs knob for AER controlling at this point.
>>>
>>> I don't want to do anything that will prevent us from adding
>>> per-device ECRC control in the future.
>>>
>>> My concern is that if we add a run-time sysfs knob in the future, the
>>> user experience on this hardware will be poor because there's no
>>> convenient path to twiddle the PCIE_ATU_TD bit when the generic code
>>> changes the AER Control bit.
>>
>> Agree.
>> Can we add it to the documentation that run time changing of ECRC settings
>> are not supported on this (i.e. Tegra194) platform (or for that matter on
>> any SoC with PCIe based on DesignWare core version 4.90A). By 'not
>> supported', I meant that the ECRC digest part may not work but the normal
>> functionality will continue to work without reporting any AER errors. I
>> tried to emulate the following scenarios on Tegra194 silicon and here are my
>> observations.
>> FWIW, I'm referring to the PCIe spec Rev 5.0 Ver 1.0 (22 May 2019)
>>
>>> What is the failure mode in these scenarios:
>>>
>>>     - User boots with defaults, ECRC is disabled.
>>>     - User enables ECRC via sysfs.
>>>     - What happens here?  ECRC is enabled via AER Control but not via
>>>       DWC TD bit.  I assume ECRC doesn't work.  Does it cause PCIe
>>>       errors (malformed TLP, etc)?
>>
>> Since DWC TD bit is not programmed, for all the transactions that go through
>> ATU, TLP Digest won't get generated (although AER registers indicate that
>> ECRC should get generated).
>> As per the spec section "2.7.1 ECRC Rules"
>>
>> ---
>> If a device Function is enabled to generate ECRC, it must calculate and
>> apply ECRC for all TLPs originated by the Function
>> ---
>>
>> So the RP would be violating the PCIe spec, but it doesn't result in any
>> error because the same section has the following rule as well
>>
>> ---
>> If a device Function is enabled to check ECRC, it must do so for all TLPs
>> with ECRC where the device is the ultimate PCI Express Receiver
>>        Note that it is still possible for the Function to receive TLPs without
>> ECRC, and these are processed normally - this is not an error
>> ---
>>
>> so, even if the EP has ECRC check enabled, because of the above rule, it
>> just processes those packets without ECRC as normal packets.
>> Basically, whoever is enabling ECRC run time gets cheated as transactions
>> routed through ATU don't really have ECRC digest
>>
>>> Or this one:
>>>
>>>     - User boots with "pci=ecrc=on", ECRC is enabled.
>>>     - ECRC works fine.
>>>     - User disables ECRC via sysfs.
>>>     - What happens here?  ECRC is disabled via AER Control, but DWC TD
>>>       bit thinks it's still enabled.
>>
>> In this case, the EP doesn't have ECRC check enabled but receives TLPs with
>> ECRC digest. This again won't result in any error because of the section
>> "2.2.3 TLP Digest Rules" which says
>>
>> ---
>> If an intermediate or ultimate PCI Express Receiver of the TLP does not
>> support ECRC checking, the Receiver must ignore the TLP Digest
>> ---
>>
>> So the EP just ignores the TLP Digest and process the TLP normally.
>> Although functionality wise there is no issue here, there could be some
>> impact on the perf because of the extra DWord data. This is again debatable
>> as the perf/data path is typically from EP's DMA engine to host system
>> memory and not config/BAR accesses.
>>>
>>> If you enabled ECRC unconditionally on DWC and the sysfs knob had no
>>> effect, I'd be OK with that.  I'm more worried about what happens when
>>> the AER bit and the DWC TD bit are set so they don't match.  What is
>>> the failure mode there?
>>
>> Based on the above experiments, we can as well keep the DWC TD bit
>> programmed unconditionally and it won't lead to any errors. As mentioned
>> before, the only downside of it is the extra DWord in each ATU routed TLP
>> which may load the bus (in downstream direction) with no real benefit as
>> such.
> 
> IIUC the issue only affects traffic from the Root Port to the
> Endpoint, and traffic going upstream is unaffected.  Here's what I
> think happens based on the RP and EP settings, please correct me if
> wrong:
> 
>    1)  RP TD+ ECRC_gen+       generates ECRC
>        EP     ECRC_check-     ignores ECRC
>        EP     ECRC_check+     checks ECRC
> 
>    2)  RP TD+ ECRC_gen-       generates ECRC when it shouldn't (defect)
>        EP     ECRC_check-     ignores ECRC
>        EP     ECRC_check+     checks ECRC (may signal errors)
> 
>    3)  RP TD- ECRC_gen+       fails to generate ECRC (defect)
>        EP     ECRC_check-     ignores ECRC
>        EP     ECRC_check+     handles TLPs without ECRC normally,
>                               but cannot detect ECRC errors
> 
>    4)  RP TD- ECRC_gen-       no ECRC generated (as expected)
>        EP     ECRC_check-     ignores ECRC
>        EP     ECRC_check+     handles TLPs without ECRC normally
> 
> If my assumptions above are correct, this defect never causes extra
> errors like Malformed TLP, etc, to be signaled regardless of the AER
> ECRC_check settings.
Yes.
> 
> The only functional problem is that in case 3, the EP *should* be able
> to check and signal ECRC errors, but it cannot because the RP doesn't
> generate ECRC.
Yes. Thats correct
> 
> Case 2 is a performance issue because we add the extra dword in every
> TLP going downstream.  That doesn't seem unreasonable since this is
> just config and BAR accesses.  The EP may detect ECRC errors when we
> don't think the RP is even generating ECRC, but in general we won't
> enable checking in the EP unless we also enable generation in the RP.
> 
> So I think setting the DWC TD bit unconditionally seems like a pretty
> good solution.
Ok. Sure. I'll push a patch to program DWC TD bit unconditionally then.
Thanks for your insights and guidance.

> 
>> Please let me know where can we go from here.
>> I can push a different patch to keep DWC TD bit always programmed if that is
>> the best approach to take at this point.
>>>
>>>>>> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
>>>>>> Reviewed-by: Jingoo Han <jingoohan1@gmail.com>
>>>>>> ---
>>>>>> V3:
>>>>>> * Added 'Reviewed-by: Jingoo Han <jingoohan1@gmail.com>'
>>>>>>
>>>>>> V2:
>>>>>> * Addressed Jingoo's review comment
>>>>>> * Removed saving 'td' bit information in 'dw_pcie' structure
>>>>>>
>>>>>>     drivers/pci/controller/dwc/pcie-designware.c | 8 ++++++--
>>>>>>     drivers/pci/controller/dwc/pcie-designware.h | 1 +
>>>>>>     2 files changed, 7 insertions(+), 2 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
>>>>>> index b5e438b70cd5..cbd651b219d2 100644
>>>>>> --- a/drivers/pci/controller/dwc/pcie-designware.c
>>>>>> +++ b/drivers/pci/controller/dwc/pcie-designware.c
>>>>>> @@ -246,6 +246,8 @@ static void dw_pcie_prog_outbound_atu_unroll(struct dw_pcie *pci, u8 func_no,
>>>>>>          dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_UPPER_TARGET,
>>>>>>                                   upper_32_bits(pci_addr));
>>>>>>          val = type | PCIE_ATU_FUNC_NUM(func_no);
>>>>>> +     if (pci->version == 0x490A)
>>>>>> +             val = val | pcie_is_ecrc_enabled() << PCIE_ATU_TD_SHIFT;
>>>>>>          val = upper_32_bits(size - 1) ?
>>>>>>                  val | PCIE_ATU_INCREASE_REGION_SIZE : val;
>>>>>>          dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_REGION_CTRL1, val);
>>>>>> @@ -294,8 +296,10 @@ static void __dw_pcie_prog_outbound_atu(struct dw_pcie *pci, u8 func_no,
>>>>>>                             lower_32_bits(pci_addr));
>>>>>>          dw_pcie_writel_dbi(pci, PCIE_ATU_UPPER_TARGET,
>>>>>>                             upper_32_bits(pci_addr));
>>>>>> -     dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, type |
>>>>>> -                        PCIE_ATU_FUNC_NUM(func_no));
>>>>>> +     val = type | PCIE_ATU_FUNC_NUM(func_no);
>>>>>> +     if (pci->version == 0x490A)
>>>>>> +             val = val | pcie_is_ecrc_enabled() << PCIE_ATU_TD_SHIFT;
>>>>>> +     dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, val);
>>>>>>          dw_pcie_writel_dbi(pci, PCIE_ATU_CR2, PCIE_ATU_ENABLE);
>>>>>>
>>>>>>          /*
>>>>>> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
>>>>>> index e7f441441db2..b01ef407fd52 100644
>>>>>> --- a/drivers/pci/controller/dwc/pcie-designware.h
>>>>>> +++ b/drivers/pci/controller/dwc/pcie-designware.h
>>>>>> @@ -89,6 +89,7 @@
>>>>>>     #define PCIE_ATU_TYPE_IO             0x2
>>>>>>     #define PCIE_ATU_TYPE_CFG0           0x4
>>>>>>     #define PCIE_ATU_TYPE_CFG1           0x5
>>>>>> +#define PCIE_ATU_TD_SHIFT            8
>>>>>>     #define PCIE_ATU_FUNC_NUM(pf)           ((pf) << 20)
>>>>>>     #define PCIE_ATU_CR2                 0x908
>>>>>>     #define PCIE_ATU_ENABLE                      BIT(31)
>>>>>> --
>>>>>> 2.17.1
>>>>>>