linux-kernel - Re: [PATCH] drm/i915: Remove unreachable code

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Date:   Mon, 1 Feb 2021 00:23:53 +0000
From:   Vinicius Tinti <viniciustinti@...il.com>
To:     Chris Wilson <chris@...is-wilson.co.uk>
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: Re: [PATCH] drm/i915: Remove unreachable code

On Sat, Jan 30, 2021 at 9:45 AM Chris Wilson <chris@...is-wilson.co.uk> wrote:
>
> Quoting Vinicius Tinti (2021-01-30 12:34:11)
> > On Fri, Jan 29, 2021 at 08:55:54PM +0000, Chris Wilson wrote:
> > > Quoting Vinicius Tinti (2021-01-29 18:15:19)
> > > > By enabling -Wunreachable-code-aggressive on Clang the following code
> > > > paths are unreachable.
> > >
> > > That code exists as commentary and, especially for sdvo, library
> > > functions that we may need in future.
> >
> > I would argue that this code could be removed since it is in git history.
> > It can be restored when needed.
> >
> > This will make the code cleaner.
>
> It doesn't change the control flow, so no complexity argument. It
> removes documentation from the code, so I have the opposite opinion.

The last change in sdvo related to this function is from commit
ce22c320b8ca ("drm/i915/sdvo: convert to encoder disable/enable"), which
dates from 2012.

It has not been used or changed for a long time. I think it could be
converted to a block comment. This will preserve the documentation
purpose. What do you think?

All this will avoid having "if (0)".

> > > The ivb-gt1 case => as we now set the gt level for ivb, should we not
> > > enable the optimisation for ivb unaffected by the w/a? Just no one has
> > > taken the time to see if it causes a regression.
> >
> > I don't know. I just found out that the code is unreachable.
> >
> > > For error state, the question remains whether we should revert to
> > > uncompressed data if the compressed stream is larger than the original.
> >
> > I don't know too.
> >
> > In this last two cases the code could be commented and the decisions
> > and problems explained in the comment section.
>
> They already are, that is the point.

I meant making them a block comment. For example:

/*
 * Enabling HiZ Raw Stall Optimization, at this point, causes corruption.
 *
 * Calling wa_masked_dis with the arguments wal, CACHE_MODE_0_GEN7,
 * HIZ_RAW_STALL_OPT_DISABLE will cause an HiZ corruption on ivb:g1.
 */

/*
 * Should fallback to uncompressed if we increase size
 * (zstream->total_out > zstream->total_in) by returning -E2BIG?
 */

> -Chris