[PATCH] PCI: j721e: Deassert PERST# after a delay of PCIE_T_PVPERL_MS ms

[PATCH] PCI: j721e: Deassert PERST# after a delay of PCIE_T_PVPERL_MS ms

[Siddharth Vadapalli]

According to Section 2.2 of the PCI Express Card Electromechanical
Specification (Revision 5.1), in order to ensure that the power and the
reference clock are stable, PERST# has to be deasserted after a delay of
100 milliseconds (TPVPERL). Currently, it is being assumed that the power
is already stable, which is not necessarily true. Hence, change the delay
to PCIE_T_PVPERL_MS to guarantee that power and reference clock are stable.

Fixes: f96b69713733 ("PCI: j721e: Use T_PERST_CLK_US macro")
Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>
---

Hello,

This patch is based on commit
c2ee9f594da8 KVM: selftests: Fix build on on non-x86 architectures
of Mainline Linux.

Regards,
Siddharth.

 drivers/pci/controller/cadence/pci-j721e.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/drivers/pci/controller/cadence/pci-j721e.c b/drivers/pci/controller/cadence/pci-j721e.c
index 284f2e0e4d26..e464cfc2c332 100644
--- a/drivers/pci/controller/cadence/pci-j721e.c
+++ b/drivers/pci/controller/cadence/pci-j721e.c
@@ -671,15 +671,14 @@ static int j721e_pcie_resume_noirq(struct device *dev)
 			return ret;
 
 		/*
-		 * The "Power Sequencing and Reset Signal Timings" table of the
-		 * PCI Express Card Electromechanical Specification, Revision
-		 * 5.1, Section 2.9.2, Symbol "T_PERST-CLK", indicates PERST#
-		 * should be deasserted after minimum of 100us once REFCLK is
-		 * stable. The REFCLK to the connector in RC mode is selected
-		 * while enabling the PHY. So deassert PERST# after 100 us.
+		 * Section 2.2 of the PCI Express Card Electromechanical
+		 * Specification (Revision 5.1) mandates that the deassertion
+		 * of the PERST# signal should be delayed by 100 ms (TPVPERL).
+		 * This shall ensure that the power and the reference clock
+		 * are stable.
 		 */
 		if (pcie->reset_gpio) {
-			fsleep(PCIE_T_PERST_CLK_US);
+			msleep(PCIE_T_PVPERL_MS);
 			gpiod_set_value_cansleep(pcie->reset_gpio, 1);
 		}
 
-- 
2.40.1

Re: [PATCH] PCI: j721e: Deassert PERST# after a delay of PCIE_T_PVPERL_MS ms

[Krzysztof Wilczyński]

Hello,

> According to Section 2.2 of the PCI Express Card Electromechanical
> Specification (Revision 5.1), in order to ensure that the power and the
> reference clock are stable, PERST# has to be deasserted after a delay of
> 100 milliseconds (TPVPERL). Currently, it is being assumed that the power
> is already stable, which is not necessarily true. Hence, change the delay
> to PCIE_T_PVPERL_MS to guarantee that power and reference clock are stable.
[...]
> This patch is based on commit
> c2ee9f594da8 KVM: selftests: Fix build on on non-x86 architectures
> of Mainline Linux.

Why KVM?  Do you have the link to this commit handy?

[...]
>  		if (pcie->reset_gpio) {
> -			fsleep(PCIE_T_PERST_CLK_US);
> +			msleep(PCIE_T_PVPERL_MS);

fsleep() with the same macro and for the same reason is also used in the
j721e_pcie_probe() callback.  I think, we would want both changed.

	Krzysztof

Re: [PATCH] PCI: j721e: Deassert PERST# after a delay of PCIE_T_PVPERL_MS ms

[Siddharth Vadapalli]

On Sat, Nov 02, 2024 at 11:19:14PM +0900, Krzysztof Wilczyński wrote:
> Hello,
> 
> > According to Section 2.2 of the PCI Express Card Electromechanical
> > Specification (Revision 5.1), in order to ensure that the power and the
> > reference clock are stable, PERST# has to be deasserted after a delay of
> > 100 milliseconds (TPVPERL). Currently, it is being assumed that the power
> > is already stable, which is not necessarily true. Hence, change the delay
> > to PCIE_T_PVPERL_MS to guarantee that power and reference clock are stable.
> [...]
> > This patch is based on commit
> > c2ee9f594da8 KVM: selftests: Fix build on on non-x86 architectures
> > of Mainline Linux.
> 
> Why KVM?  Do you have the link to this commit handy?

Since this is a fix, I had based the patch on the latest Mainline Linux
with the head corresponding to the aforementioned commit. Link:
https://github.com/torvalds/linux/commit/c2ee9f594da8

> 
> [...]
> >  		if (pcie->reset_gpio) {
> > -			fsleep(PCIE_T_PERST_CLK_US);
> > +			msleep(PCIE_T_PVPERL_MS);
> 
> fsleep() with the same macro and for the same reason is also used in the
> j721e_pcie_probe() callback.  I think, we would want both changed.

Thank you for pointing this out. I will update it in the v2 patch.

Regards,
Siddharth.