linux-kernel - Re: [PATCH v3 0/2] Tango PCIe controller support

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Message-ID: <88af8239-bef4-dfd5-2280-66104bee72e8@free.fr>
Date:   Sat, 1 Apr 2017 00:05:27 +0200
From:   Mason <slash.tmp@...e.fr>
To:     linux-pci <linux-pci@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Cc:     Marc Gonzalez <marc_gonzalez@...madesigns.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Liviu Dudau <liviu.dudau@....com>,
        David Laight <david.laight@...lab.com>,
        Thibaud Cornic <thibaud_cornic@...madesigns.com>,
        Phuong Nguyen <phuong_nguyen@...madesigns.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 0/2] Tango PCIe controller support

On 30/03/2017 22:56, Mason wrote:

> I've run into an issue.
> 
> If I boot the system with earlyprintk enabled (as I've
> been doing throughout my dev), things work as expected.
> 
> But if I boot with earlyprintk disabled, then the system
> does not "see" the PCIe board, because reading the vendor
> ID returns 0xffffffff.
> 
> What we think is happening, is that when earlyprintk is
> disabled, the system proceeds much faster through the
> various inits, and the PCIe init happens when PCIe
> link training has not completed yet.
> 
> If that is the case, then it seems I would need to check
> the link state in my probe function.

I determined empirically that link training takes around
10-15 ms. Though I suppose this might depend on the
specific PCIe board? (I'm only considering x1 link.)

So I added an msleep(20); in the probe function, and in
the config_read callback, I check the link status on the
first read to the device.

Should I msleep(40) to be safe?

Regards.