linux-kernel - Re: [PATCH] drm/bochs: add edid present check

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Message-ID: <20181219152129.k7v4ttpsazguswke@sirius.home.kraxel.org>
Date:   Wed, 19 Dec 2018 16:21:29 +0100
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     Oleksandr Andrushchenko <andr2000@...il.com>
Cc:     dri-devel@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:DRM DRIVER FOR BOCHS VIRTUAL GPU" 
        <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH] drm/bochs: add edid present check

  Hi,

> You could probably have a comment here explaining the magic below
> (just like in the commit message to ease the task of understanding
> while reading the code why 2 of 8 bytes of the EDID header is checked
> and why it is all needed). Of course one can use git blame... Up to you

Makes sense.

> > +	if (readb(bochs->mmio + 0) != 0x00 ||
> > +	    readb(bochs->mmio + 1) != 0xff)
> 
> bochs->mmio is defined as "void __iomem   *mmio;". Can we please avoid
> void pointer arithmetic here?

Why is that a problem?  gcc uses bytes when doing pointer arithmetic
with void pointers (even though it is undefined in the C standard),
and as far I know the linux kernel depends on that behavior anyway.

Also the driver already does it everywhere.

cheers,
  Gerd