[PATCH] PCI: qcom: Fix warning generated due to the incorrect data type

[PATCH] PCI: qcom: Fix warning generated due to the incorrect data type

[Manivannan Sadhasivam]

Fix the below sparse warning due to the use of incorrect initializer
data type (u16) for bdf_be variable that receives the return value of
cpu_to_be16(). The correct type should be __be16.

sparse warnings: (new ones prefixed by >>)
>> drivers/pci/controller/dwc/pcie-qcom.c:1305:30: sparse: sparse: incorrect type in initializer (different base types) @@     expected unsigned short [usertype] bdf_be @@     got restricted __be16 [usertype] @@
   drivers/pci/controller/dwc/pcie-qcom.c:1305:30: sparse:     expected unsigned short [usertype] bdf_be
   drivers/pci/controller/dwc/pcie-qcom.c:1305:30: sparse:     got restricted __be16 [usertype]

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
---
 drivers/pci/controller/dwc/pcie-qcom.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
index 8a7a300163e5..6c3b034e9946 100644
--- a/drivers/pci/controller/dwc/pcie-qcom.c
+++ b/drivers/pci/controller/dwc/pcie-qcom.c
@@ -1312,7 +1312,7 @@ static int qcom_pcie_config_sid_sm8250(struct qcom_pcie *pcie)
 
 	/* Look for an available entry to hold the mapping */
 	for (i = 0; i < nr_map; i++) {
-		u16 bdf_be = cpu_to_be16(map[i].bdf);
+		__be16 bdf_be = cpu_to_be16(map[i].bdf);
 		u32 val;
 		u8 hash;
 
-- 
2.25.1

Re: [PATCH] PCI: qcom: Fix warning generated due to the incorrect data type

[Bjorn Helgaas]

On Wed, Nov 24, 2021 at 07:34:24PM +0530, Manivannan Sadhasivam wrote:
> Fix the below sparse warning due to the use of incorrect initializer
> data type (u16) for bdf_be variable that receives the return value of
> cpu_to_be16(). The correct type should be __be16.

I think the patch looks OK, but the reason to change this is not to
"fix the warning".  The reason is to fix the *problem*, i.e.,
cpu_to_be16() returns "__be16", which is incompatible with "u16".

The warning is only a helpful hint, and should not be part of the
subject line.  "cpu_to_be16" or "iommu-map" would be much more
useful information in the subject.

I'm also curious why pcie-qcom.c is the only driver that does this.
"iommu-map" is not specific to qcom, but no other drivers do similar
things with it.

> sparse warnings: (new ones prefixed by >>)
> >> drivers/pci/controller/dwc/pcie-qcom.c:1305:30: sparse: sparse: incorrect type in initializer (different base types) @@     expected unsigned short [usertype] bdf_be @@     got restricted __be16 [usertype] @@
>    drivers/pci/controller/dwc/pcie-qcom.c:1305:30: sparse:     expected unsigned short [usertype] bdf_be
>    drivers/pci/controller/dwc/pcie-qcom.c:1305:30: sparse:     got restricted __be16 [usertype]
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> ---
>  drivers/pci/controller/dwc/pcie-qcom.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index 8a7a300163e5..6c3b034e9946 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -1312,7 +1312,7 @@ static int qcom_pcie_config_sid_sm8250(struct qcom_pcie *pcie)
>  
>  	/* Look for an available entry to hold the mapping */
>  	for (i = 0; i < nr_map; i++) {
> -		u16 bdf_be = cpu_to_be16(map[i].bdf);
> +		__be16 bdf_be = cpu_to_be16(map[i].bdf);
>  		u32 val;
>  		u8 hash;
>  
> -- 
> 2.25.1
> 

Re: [PATCH] PCI: qcom: Fix warning generated due to the incorrect data type

[Manivannan Sadhasivam]

Hi Bjorn,

On Mon, Nov 29, 2021 at 09:36:14PM -0600, Bjorn Helgaas wrote:
> On Wed, Nov 24, 2021 at 07:34:24PM +0530, Manivannan Sadhasivam wrote:
> > Fix the below sparse warning due to the use of incorrect initializer
> > data type (u16) for bdf_be variable that receives the return value of
> > cpu_to_be16(). The correct type should be __be16.
> 
> I think the patch looks OK, but the reason to change this is not to
> "fix the warning".  The reason is to fix the *problem*, i.e.,
> cpu_to_be16() returns "__be16", which is incompatible with "u16".
> 
> The warning is only a helpful hint, and should not be part of the
> subject line.  "cpu_to_be16" or "iommu-map" would be much more
> useful information in the subject.
> 

okay

> I'm also curious why pcie-qcom.c is the only driver that does this.
> "iommu-map" is not specific to qcom, but no other drivers do similar
> things with it.
> 

Yes, on the recent qcom platforms starting from sm8250 we need to program
the BDF to SID mapping in the controller and that's the reason we are
extracting the "iommu-map" property in DT.

Thanks,
Mani

> > sparse warnings: (new ones prefixed by >>)
> > >> drivers/pci/controller/dwc/pcie-qcom.c:1305:30: sparse: sparse: incorrect type in initializer (different base types) @@     expected unsigned short [usertype] bdf_be @@     got restricted __be16 [usertype] @@
> >    drivers/pci/controller/dwc/pcie-qcom.c:1305:30: sparse:     expected unsigned short [usertype] bdf_be
> >    drivers/pci/controller/dwc/pcie-qcom.c:1305:30: sparse:     got restricted __be16 [usertype]
> > 
> > Reported-by: kernel test robot <lkp@intel.com>
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> > ---
> >  drivers/pci/controller/dwc/pcie-qcom.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> > index 8a7a300163e5..6c3b034e9946 100644
> > --- a/drivers/pci/controller/dwc/pcie-qcom.c
> > +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> > @@ -1312,7 +1312,7 @@ static int qcom_pcie_config_sid_sm8250(struct qcom_pcie *pcie)
> >  
> >  	/* Look for an available entry to hold the mapping */
> >  	for (i = 0; i < nr_map; i++) {
> > -		u16 bdf_be = cpu_to_be16(map[i].bdf);
> > +		__be16 bdf_be = cpu_to_be16(map[i].bdf);
> >  		u32 val;
> >  		u8 hash;
> >  
> > -- 
> > 2.25.1
> > 

Re: [PATCH] PCI: qcom: Fix warning generated due to the incorrect data type

[Bjorn Helgaas]

[+cc Marc, Alyssa, Sven for RID-to-SID mapping insight.  The patch at
https://lore.kernel.org/all/20211130062137.GD205712@thinkpad/ merely
fixes a warning.  My meta-question is about the qcom BDF-to-SID
mapping.]

On Tue, Nov 30, 2021 at 11:51:37AM +0530, Manivannan Sadhasivam wrote:
> On Mon, Nov 29, 2021 at 09:36:14PM -0600, Bjorn Helgaas wrote:
> > ...
> > I'm also curious why pcie-qcom.c is the only driver that does this.
> > "iommu-map" is not specific to qcom, but no other drivers do similar
> > things with it.
> 
> Yes, on the recent qcom platforms starting from sm8250 we need to program
> the BDF to SID mapping in the controller and that's the reason we are
> extracting the "iommu-map" property in DT.

This sounds like something that may not really be specific to sm8250.

It looks vaguely similar to apple_pcie_add_device().  Compare the qcom
code at [1] with the Apple code at [2].

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pci/controller/dwc/pcie-qcom.c?id=v5.16-rc1#n1308
[2] https://git.kernel.org/linus/468c8d52c332

> > > sparse warnings: (new ones prefixed by >>)
> > > >> drivers/pci/controller/dwc/pcie-qcom.c:1305:30: sparse: sparse: incorrect type in initializer (different base types) @@     expected unsigned short [usertype] bdf_be @@     got restricted __be16 [usertype] @@
> > >    drivers/pci/controller/dwc/pcie-qcom.c:1305:30: sparse:     expected unsigned short [usertype] bdf_be
> > >    drivers/pci/controller/dwc/pcie-qcom.c:1305:30: sparse:     got restricted __be16 [usertype]
> > > 
> > > Reported-by: kernel test robot <lkp@intel.com>
> > > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> > > ---
> > >  drivers/pci/controller/dwc/pcie-qcom.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> > > index 8a7a300163e5..6c3b034e9946 100644
> > > --- a/drivers/pci/controller/dwc/pcie-qcom.c
> > > +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> > > @@ -1312,7 +1312,7 @@ static int qcom_pcie_config_sid_sm8250(struct qcom_pcie *pcie)
> > >  
> > >  	/* Look for an available entry to hold the mapping */
> > >  	for (i = 0; i < nr_map; i++) {
> > > -		u16 bdf_be = cpu_to_be16(map[i].bdf);
> > > +		__be16 bdf_be = cpu_to_be16(map[i].bdf);
> > >  		u32 val;
> > >  		u8 hash;
> > >  
> > > -- 
> > > 2.25.1
> > > 

Re: [PATCH] PCI: qcom: Fix warning generated due to the incorrect data type

[Sven Peter]

Hi,

On Tue, Nov 30, 2021, at 17:03, Bjorn Helgaas wrote:
> [+cc Marc, Alyssa, Sven for RID-to-SID mapping insight.  The patch at
> https://lore.kernel.org/all/20211130062137.GD205712@thinkpad/ merely
> fixes a warning.  My meta-question is about the qcom BDF-to-SID
> mapping.]
>
> On Tue, Nov 30, 2021 at 11:51:37AM +0530, Manivannan Sadhasivam wrote:
>> On Mon, Nov 29, 2021 at 09:36:14PM -0600, Bjorn Helgaas wrote:
>> > ...
>> > I'm also curious why pcie-qcom.c is the only driver that does this.
>> > "iommu-map" is not specific to qcom, but no other drivers do similar
>> > things with it.
>> 
>> Yes, on the recent qcom platforms starting from sm8250 we need to program
>> the BDF to SID mapping in the controller and that's the reason we are
>> extracting the "iommu-map" property in DT.
>
> This sounds like something that may not really be specific to sm8250.

So a single IOMMU can possibly differentiate between N different devices [1].
Each device [1] is identified by some number which is called sid (stream id?
security id? who knows.) on Apple hardware (and apparently also on qcom).
Now I don't know much about PCI but the way I understand it is that the
bus/device/function tuple can be used to uniquely identify a single device on the bus.
All iommu-map does is to provide the mapping between those two different spaces [2].

For most iommus this seems to be just a static mapping that's hardwired in silicon
and I think that's why almost no PCI driver needs to care about it: The iommu
core will just use it to convert the PCI requester ID to a number the iommu
driver understands.

Apple's frankenchip however allows to configure this mapping from software
after a device has been attached and that's why we need that special code inside
the PCI driver: We have to make sure that whatever is configured inside iommu-map
(and used by the iommu core to match PCI devices to iommu groups) matches to what
the HW does.

I can only assume that qcom does something similar. It looks like the qcom HW can be
fully configured during probe time though while we really have to wait until a device
is attached for the Apple chip (mostly because we only have 16 slots there).


Hope that helps.


Best,

Sven



[1] Technically the smallest unit are iommu groups which can contain multiple
devices but we can just ignore that. The iommu code will do the correct thing
if it gets told that two PCI devices have the same identification number.

[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/iommu/of_iommu.c#n53

Re: [PATCH] PCI: qcom: Fix warning generated due to the incorrect data type

[Marc Zyngier]

On Tue, 30 Nov 2021 16:03:38 +0000,
Bjorn Helgaas <helgaas@kernel.org> wrote:
> 
> [+cc Marc, Alyssa, Sven for RID-to-SID mapping insight.  The patch at
> https://lore.kernel.org/all/20211130062137.GD205712@thinkpad/ merely
> fixes a warning.  My meta-question is about the qcom BDF-to-SID
> mapping.]
> 
> On Tue, Nov 30, 2021 at 11:51:37AM +0530, Manivannan Sadhasivam wrote:
> > On Mon, Nov 29, 2021 at 09:36:14PM -0600, Bjorn Helgaas wrote:
> > > ...
> > > I'm also curious why pcie-qcom.c is the only driver that does this.
> > > "iommu-map" is not specific to qcom, but no other drivers do similar
> > > things with it.
> > 
> > Yes, on the recent qcom platforms starting from sm8250 we need to program
> > the BDF to SID mapping in the controller and that's the reason we are
> > extracting the "iommu-map" property in DT.
> 
> This sounds like something that may not really be specific to sm8250.
> 
> It looks vaguely similar to apple_pcie_add_device().  Compare the qcom
> code at [1] with the Apple code at [2].

It looks indeed similar in spirit, though the implementation seems
different. The qcom code seems to brute-force the mappings upfront,
while the apple driver relies on bus notifiers to map things on
demand.

The annoying thing with these blocks is that they are neither part of
the IOMMU nor the PCIe block. It is just a piece of glue logic in
the middle...

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.