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

From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Roger Pau Monne <roger.pau@citrix.com>
Cc: linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org,
	Andy Shevchenko <andy@kernel.org>,
	Mika Westerberg <mika.westerberg@linux.intel.com>,
	Linus Walleij <linus.walleij@linaro.org>,
	linux-gpio@vger.kernel.org
Subject: Re: [PATCH v2 1/2] intel/pinctrl: check REVID register value for device presence
Date: Wed, 24 Mar 2021 19:01:18 +0200	[thread overview]
Message-ID: <YFtwXj1Q+PRO0asv@smile.fi.intel.com> (raw)
In-Reply-To: <20210324154312.61878-2-roger.pau@citrix.com>

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@kernel.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