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

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Date:   Thu, 25 Mar 2021 09:36:26 +0100
From:   Roger Pau Monné <roger.pau@...rix.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.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 07:01:18PM +0200, Andy Shevchenko wrote:
> 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?

Hm, I haven't seen those issues up until 91d898e51e60 ('pinctrl:
intel: Convert capability list to features'), but the device wasn't
working properly for sure, as the registers where not accessible, it
just didn't lead to a kernel crash.

> ...
> 
> > 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.

I just used the same as the one that's on the MAINTAINERS file,
because I already had that n my Cc list. I can change to the @intel
one if that's your preference.

> ...
> 
> >  		/* 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.

Right, will change and send v3.

Thanks.