linux-kernel - Re: [PATCH v2] PCI: dra7xx: Fix reset behaviour

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Message-ID: <20210622115604.GA25503@lpieralisi>
Date:   Tue, 22 Jun 2021 12:56:04 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Pali Rohár <pali@...nel.org>,
        linus.walleij@...aro.org, kishon@...com
Cc:     Luca Ceresoli <luca@...aceresoli.net>, linux-pci@...r.kernel.org,
        linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH v2] PCI: dra7xx: Fix reset behaviour

[Adding Linus for GPIO discussion, thread:
https://lore.kernel.org/linux-pci/20210531090540.2663171-1-luca@lucaceresoli.net]

On Tue, Jun 22, 2021 at 01:06:27PM +0200, Pali Rohár wrote:
> Hello!
> 
> On Tuesday 22 June 2021 12:57:22 Luca Ceresoli wrote:
> > Nothing happened after a few weeks... I understand that knowing the
> > correct reset timings is relevant, but unfortunately I cannot help much
> > in finding out the correct values.
> > 
> > However I'm wondering what should happen to this patch. It *does* fix a
> > real bug, but potentially with an incorrect or non-optimal usleep range.
> > Do we really want to ignore a bugfix because we are not sure about how
> > long this delay should be?
> 
> As there is no better solution right now, I'm fine with your patch. But
> patch needs to be approved by Lorenzo, so please wait for his final
> answer.

I am not a GPIO expert and I have a feeling this is platform specific
beyond what the PCI specification can actually define architecturally.

There are two things I'd like to see:

1) If Linus can have a look at the GPIO bits in this thread that would
   definitely help clarify any pending controversy
2) Kishon to test on *existing* platforms and confirm there are no
   regressions triggered

> I would suggest to add a comment for call "usleep_range(1000, 2000);"
> that you have chosen some "random" values which worked fine on your
> setup and that they fix mentioned bug. Comment just to mark this sleep
> code that is suboptimal / not-so-correct and to prevent other people to
> copy+paste this code into other (new) drivers...

Yes a comment would help but as I say above I am afraid this is
a platform specific set-up, ie that delay is somewhat tied to
a platform, not sure there is anything we can do.

If Linus and Kishon are happy with the approach we can merge this
patch.

Lorenzo