linux-kernel - Re: [Intel-gfx] [PATCH RESEND] drm/i915: Fix pipe/transcoder enum mismatches

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Date:   Fri, 5 May 2017 12:12:49 -0700
From:   Grant Grundler <grundler@...omium.org>
To:     Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:     Matthias Kaehlcke <mka@...omium.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        David Airlie <airlied@...ux.ie>,
        Grant Grundler <grundler@...omium.org>,
        intel-gfx@...ts.freedesktop.org,
        LKML <linux-kernel@...r.kernel.org>,
        Greg Hackmann <ghackmann@...gle.com>,
        Michael Davidson <md@...gle.com>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH RESEND] drm/i915: Fix pipe/transcoder enum mismatches

On Fri, May 5, 2017 at 10:40 AM, Ville Syrjälä
<ville.syrjala@...ux.intel.com> wrote:
> On Fri, May 05, 2017 at 10:26:36AM -0700, Matthias Kaehlcke wrote:
>> El Thu, Apr 20, 2017 at 02:56:05PM -0700 Matthias Kaehlcke ha dit:
>>
>> > In several instances the driver passes an 'enum pipe' value to a
>> > function expecting an 'enum transcoder' and viceversa. Since PIPE_x and
>> > TRANSCODER_x have the same values this doesn't cause functional
>> > problems. Still it is incorrect and causes clang to generate warnings
>> > like this:
>> >
>> > drivers/gpu/drm/i915/intel_display.c:1844:34: warning: implicit
>> >   conversion from enumeration type 'enum transcoder' to different
>> >   enumeration type 'enum pipe' [-Wenum-conversion]
>> >     assert_fdi_rx_enabled(dev_priv, TRANSCODER_A);
>> >
>> > Change the code to pass values of the type expected by the callee.
>> >
>> > Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
>> > ---
>> >  drivers/gpu/drm/i915/intel_display.c | 4 ++--
>> >  drivers/gpu/drm/i915/intel_dp.c      | 6 ++++--
>> >  drivers/gpu/drm/i915/intel_hdmi.c    | 6 ++++--
>> >  drivers/gpu/drm/i915/intel_sdvo.c    | 6 ++++--
>> >  4 files changed, 14 insertions(+), 8 deletions(-)
>>
>> Ping, any comments on this patch?
>
> I'm not convinced the patch is making things any better really. To
> fix this really properly, I think we'd need to introduce a new enum
> pch_transcoder and thus avoid the confusion of which type of
> transcoder we're talking about.

Is an enum better than coding an explicit conversion in an inline function?
Then the code can do some sanity checking as well. Something like:

enum transcoder pch_to_cpu_enum(enum pipe)
{
    WARN_ON(pipe > FOO);
    return (enum transcoder) pipe;
}

> Currently most places expect an
> enum pipe when dealing with PCH transcoders, and enum transcoder
> when dealing with CPU transcoders. But there are some exceptions
> of course.

cheers,
grant
>
> --
> Ville Syrjälä
> Intel OTC