[PATCH v2] PCI: aardvark: Wait for endpoint to be ready before training link

[PATCH v2] PCI: aardvark: Wait for endpoint to be ready before training link

[Remi Pommarel]

When configuring pcie reset pin from gpio (e.g. initially set by
u-boot) to pcie function this pin goes low for a brief moment
asserting the PERST# signal. Thus connected device enters fundamental
reset process and link configuration can only begin after a minimal
100ms delay (see [1]).

Because the pin configuration comes from the "default" pinctrl it is
implicitly configured before the probe callback is called:

driver_probe_device()
  really_probe()
    ...
    pinctrl_bind_pins() /* Here pin goes from gpio to PCIE reset
                           function and PERST# is asserted */
    ...
    drv->probe()

[1] "PCI Express Base Specification", REV. 4.0
    PCI Express, February 19 2014, 6.6.1 Conventional Reset

Signed-off-by: Remi Pommarel <repk@triplefau.lt>
---
Changes since v1:
  - Add a comment about pinctrl implicit pin configuration
  - Use more legible msleep
  - Use PCI_PM_D3COLD_WAIT macro

Please note that I will unlikely be able to answer any comments from May
24th to June 10th.
---
 drivers/pci/controller/pci-aardvark.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
index 134e0306ff00..d998c2b9cd04 100644
--- a/drivers/pci/controller/pci-aardvark.c
+++ b/drivers/pci/controller/pci-aardvark.c
@@ -324,6 +324,14 @@ static void advk_pcie_setup_hw(struct advk_pcie *pcie)
 	reg |= PIO_CTRL_ADDR_WIN_DISABLE;
 	advk_writel(pcie, reg, PIO_CTRL);
 
+	/*
+	 * PERST# signal could have been asserted by pinctrl subsystem before
+	 * probe() callback has been called, making the endpoint going into
+	 * fundamental reset. As required by PCI Express spec a delay for at
+	 * least 100ms after such a reset before link training is needed.
+	 */
+	msleep(PCI_PM_D3COLD_WAIT);
+
 	/* Start link training */
 	reg = advk_readl(pcie, PCIE_CORE_LINK_CTRL_STAT_REG);
 	reg |= PCIE_CORE_LINK_TRAINING;
-- 
2.20.1

Re: [PATCH v2] PCI: aardvark: Wait for endpoint to be ready before training link

[Remi Pommarel]

On Wed, May 22, 2019 at 11:33:50PM +0200, Remi Pommarel wrote:
> When configuring pcie reset pin from gpio (e.g. initially set by
> u-boot) to pcie function this pin goes low for a brief moment
> asserting the PERST# signal. Thus connected device enters fundamental
> reset process and link configuration can only begin after a minimal
> 100ms delay (see [1]).
> 
> Because the pin configuration comes from the "default" pinctrl it is
> implicitly configured before the probe callback is called:
> 
> driver_probe_device()
>   really_probe()
>     ...
>     pinctrl_bind_pins() /* Here pin goes from gpio to PCIE reset
>                            function and PERST# is asserted */
>     ...
>     drv->probe()
> 
> [1] "PCI Express Base Specification", REV. 4.0
>     PCI Express, February 19 2014, 6.6.1 Conventional Reset
> 
> Signed-off-by: Remi Pommarel <repk@triplefau.lt>
> ---
> Changes since v1:
>   - Add a comment about pinctrl implicit pin configuration
>   - Use more legible msleep
>   - Use PCI_PM_D3COLD_WAIT macro
> 
> Please note that I will unlikely be able to answer any comments from May
> 24th to June 10th.
> ---
>  drivers/pci/controller/pci-aardvark.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> index 134e0306ff00..d998c2b9cd04 100644
> --- a/drivers/pci/controller/pci-aardvark.c
> +++ b/drivers/pci/controller/pci-aardvark.c
> @@ -324,6 +324,14 @@ static void advk_pcie_setup_hw(struct advk_pcie *pcie)
>  	reg |= PIO_CTRL_ADDR_WIN_DISABLE;
>  	advk_writel(pcie, reg, PIO_CTRL);
>  
> +	/*
> +	 * PERST# signal could have been asserted by pinctrl subsystem before
> +	 * probe() callback has been called, making the endpoint going into
> +	 * fundamental reset. As required by PCI Express spec a delay for at
> +	 * least 100ms after such a reset before link training is needed.
> +	 */
> +	msleep(PCI_PM_D3COLD_WAIT);
> +
>  	/* Start link training */
>  	reg = advk_readl(pcie, PCIE_CORE_LINK_CTRL_STAT_REG);
>  	reg |= PCIE_CORE_LINK_TRAINING;
> -- 
> 2.20.1

Gentle ping.

-- 
Remi

Re: [PATCH v2] PCI: aardvark: Wait for endpoint to be ready before training link

[Lorenzo Pieralisi]

On Tue, Aug 06, 2019 at 08:49:46PM +0200, Remi Pommarel wrote:
> On Wed, May 22, 2019 at 11:33:50PM +0200, Remi Pommarel wrote:
> > When configuring pcie reset pin from gpio (e.g. initially set by
> > u-boot) to pcie function this pin goes low for a brief moment
> > asserting the PERST# signal. Thus connected device enters fundamental
> > reset process and link configuration can only begin after a minimal
> > 100ms delay (see [1]).
> > 
> > Because the pin configuration comes from the "default" pinctrl it is
> > implicitly configured before the probe callback is called:
> > 
> > driver_probe_device()
> >   really_probe()
> >     ...
> >     pinctrl_bind_pins() /* Here pin goes from gpio to PCIE reset
> >                            function and PERST# is asserted */
> >     ...
> >     drv->probe()
> > 
> > [1] "PCI Express Base Specification", REV. 4.0
> >     PCI Express, February 19 2014, 6.6.1 Conventional Reset
> > 
> > Signed-off-by: Remi Pommarel <repk@triplefau.lt>
> > ---
> > Changes since v1:
> >   - Add a comment about pinctrl implicit pin configuration
> >   - Use more legible msleep
> >   - Use PCI_PM_D3COLD_WAIT macro
> > 
> > Please note that I will unlikely be able to answer any comments from May
> > 24th to June 10th.
> > ---
> >  drivers/pci/controller/pci-aardvark.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> > index 134e0306ff00..d998c2b9cd04 100644
> > --- a/drivers/pci/controller/pci-aardvark.c
> > +++ b/drivers/pci/controller/pci-aardvark.c
> > @@ -324,6 +324,14 @@ static void advk_pcie_setup_hw(struct advk_pcie *pcie)
> >  	reg |= PIO_CTRL_ADDR_WIN_DISABLE;
> >  	advk_writel(pcie, reg, PIO_CTRL);
> >  
> > +	/*
> > +	 * PERST# signal could have been asserted by pinctrl subsystem before
> > +	 * probe() callback has been called, making the endpoint going into
> > +	 * fundamental reset. As required by PCI Express spec a delay for at
> > +	 * least 100ms after such a reset before link training is needed.
> > +	 */
> > +	msleep(PCI_PM_D3COLD_WAIT);
> > +
> >  	/* Start link training */
> >  	reg = advk_readl(pcie, PCIE_CORE_LINK_CTRL_STAT_REG);
> >  	reg |= PCIE_CORE_LINK_TRAINING;
> > -- 
> > 2.20.1
> 
> Gentle ping.

Thomas, sorry for the delay, unless you object I would merge this
patch, I need your ACK to proceed though.

Thanks,
Lorenzo

Re: [PATCH v2] PCI: aardvark: Wait for endpoint to be ready before training link

[Thomas Petazzoni]

Hello Remi,

On Wed, 22 May 2019 23:33:50 +0200
Remi Pommarel <repk@triplefau.lt> wrote:

> When configuring pcie reset pin from gpio (e.g. initially set by
> u-boot) to pcie function this pin goes low for a brief moment
> asserting the PERST# signal. Thus connected device enters fundamental
> reset process and link configuration can only begin after a minimal
> 100ms delay (see [1]).
> 
> Because the pin configuration comes from the "default" pinctrl it is
> implicitly configured before the probe callback is called:
> 
> driver_probe_device()
>   really_probe()
>     ...
>     pinctrl_bind_pins() /* Here pin goes from gpio to PCIE reset
>                            function and PERST# is asserted */
>     ...
>     drv->probe()
> 
> [1] "PCI Express Base Specification", REV. 4.0
>     PCI Express, February 19 2014, 6.6.1 Conventional Reset
> 
> Signed-off-by: Remi Pommarel <repk@triplefau.lt>

It is always a bit annoying to add another 100ms in the boot path, but
I don't see an easy alternative solution, so:

Acked-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

Re: [PATCH v2] PCI: aardvark: Wait for endpoint to be ready before training link

[Lorenzo Pieralisi]

On Wed, May 22, 2019 at 11:33:50PM +0200, Remi Pommarel wrote:
> When configuring pcie reset pin from gpio (e.g. initially set by
> u-boot) to pcie function this pin goes low for a brief moment
> asserting the PERST# signal. Thus connected device enters fundamental
> reset process and link configuration can only begin after a minimal
> 100ms delay (see [1]).
> 
> Because the pin configuration comes from the "default" pinctrl it is
> implicitly configured before the probe callback is called:
> 
> driver_probe_device()
>   really_probe()
>     ...
>     pinctrl_bind_pins() /* Here pin goes from gpio to PCIE reset
>                            function and PERST# is asserted */
>     ...
>     drv->probe()
> 
> [1] "PCI Express Base Specification", REV. 4.0
>     PCI Express, February 19 2014, 6.6.1 Conventional Reset
> 
> Signed-off-by: Remi Pommarel <repk@triplefau.lt>
> ---
> Changes since v1:
>   - Add a comment about pinctrl implicit pin configuration
>   - Use more legible msleep
>   - Use PCI_PM_D3COLD_WAIT macro
> 
> Please note that I will unlikely be able to answer any comments from May
> 24th to June 10th.
> ---
>  drivers/pci/controller/pci-aardvark.c | 8 ++++++++
>  1 file changed, 8 insertions(+)

Applied to pci/aardvark, thanks.

Lorenzo

> diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> index 134e0306ff00..d998c2b9cd04 100644
> --- a/drivers/pci/controller/pci-aardvark.c
> +++ b/drivers/pci/controller/pci-aardvark.c
> @@ -324,6 +324,14 @@ static void advk_pcie_setup_hw(struct advk_pcie *pcie)
>  	reg |= PIO_CTRL_ADDR_WIN_DISABLE;
>  	advk_writel(pcie, reg, PIO_CTRL);
>  
> +	/*
> +	 * PERST# signal could have been asserted by pinctrl subsystem before
> +	 * probe() callback has been called, making the endpoint going into
> +	 * fundamental reset. As required by PCI Express spec a delay for at
> +	 * least 100ms after such a reset before link training is needed.
> +	 */
> +	msleep(PCI_PM_D3COLD_WAIT);
> +
>  	/* Start link training */
>  	reg = advk_readl(pcie, PCIE_CORE_LINK_CTRL_STAT_REG);
>  	reg |= PCIE_CORE_LINK_TRAINING;
> -- 
> 2.20.1
>