linux-kernel - Re: [PATCH] PCI: j721e: Deassert PERST# after a delay of PCIE_T_PVPERL

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Message-ID: <f2af6cea-8365-42eb-be53-634eb0fe7cab@ti.com>
Date: Mon, 4 Nov 2024 12:38:20 +0530
From: Siddharth Vadapalli <s-vadapalli@...com>
To: Krzysztof Wilczyński <kw@...ux.com>
CC: Siddharth Vadapalli <s-vadapalli@...com>, <bhelgaas@...gle.com>,
        <lpieralisi@...nel.org>, <robh@...nel.org>, <vigneshr@...com>,
        <manivannan.sadhasivam@...aro.org>, <thomas.richard@...tlin.com>,
        <linux-omap@...r.kernel.org>, <linux-pci@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
        <srk@...com>
Subject: Re: [PATCH] PCI: j721e: Deassert PERST# after a delay of
 PCIE_T_PVPERL_MS ms

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.