linux-kernel - Re: [PATCH v2 1/2] intel/pinctrl: check REVID register value for device presence

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Date:   Wed, 24 Mar 2021 19:01:18 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Roger Pau Monne <roger.pau@...rix.com>
Cc:     linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
        Andy Shevchenko <andy@...nel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-gpio@...r.kernel.org
Subject: Re: [PATCH v2 1/2] intel/pinctrl: check REVID register value for
 device presence

On Wed, Mar 24, 2021 at 04:43:11PM +0100, Roger Pau Monne wrote:

Thanks for a fix! My comments below.

> Use the value read from the REVID register in order to check for the
> presence of the device. A read of all ones is treated as if the device
> is not present, and hence probing is ended.
> 
> This fixes an issue when running as a Xen PVH dom0, where the ACPI
> DSDT table is provided unmodified to dom0 and hence contains the
> pinctrl devices, but the MMIO region(s) containing the device
> registers might not be mapped in the guest physical memory map if such
> region(s) are not exposed on a PCI device BAR or marked as reserved in
> the host memory map.

Any particular point that we can use in the Fixes tag?

...

> Suggested-by: Andy Shevchenko <andy@...nel.org>

Hmm... was it that address I have used? In any case I think my @linux.intel.com
is better.

...

>  		/* Determine community features based on the revision */
>  		value = readl(regs + REVID);
> +		if (value == ~0u)
> +			return -ENODATA;

I think -ENODEV is more appropriate here.
Also comment above should be adjusted to explain this check.

-- 
With Best Regards,
Andy Shevchenko