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

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Message-ID: <20191014212938.14516102@windsurf.home>
Date:   Mon, 14 Oct 2019 21:29:38 +0200
From:   Thomas Petazzoni <thomas.petazzoni@...tlin.com>
To:     Remi Pommarel <repk@...plefau.lt>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Ellie Reeves <ellierevves@...il.com>,
        linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] PCI: aardvark: Wait for endpoint to be ready before
 training link

Hello Remi,

On Wed, 22 May 2019 23:33:50 +0200
Remi Pommarel <repk@...plefau.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@...plefau.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@...tlin.com>

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