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Message-ID: <20191210095241.GO624164@phenom.ffwll.local>
Date: Tue, 10 Dec 2019 10:52:41 +0100
From: Daniel Vetter <daniel@...ll.ch>
To: Benjamin GAIGNARD <benjamin.gaignard@...com>
Cc: Jani Nikula <jani.nikula@...ux.intel.com>,
Thomas Zimmermann <tzimmermann@...e.de>,
"maarten.lankhorst@...ux.intel.com"
<maarten.lankhorst@...ux.intel.com>,
"mripard@...nel.org" <mripard@...nel.org>,
"sean@...rly.run" <sean@...rly.run>,
"airlied@...ux.ie" <airlied@...ux.ie>,
"daniel@...ll.ch" <daniel@...ll.ch>,
"yakui.zhao@...el.com" <yakui.zhao@...el.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH] drm/modes: remove unused variables
On Thu, Dec 05, 2019 at 10:23:51AM +0000, Benjamin GAIGNARD wrote:
> + Zhao Yakui
>
> On 12/5/19 10:55 AM, Jani Nikula wrote:
> > On Wed, 04 Dec 2019, Benjamin GAIGNARD <benjamin.gaignard@...com> wrote:
> >> On 12/4/19 10:35 AM, Thomas Zimmermann wrote:
> >>> Hi
> >>>
> >>> Am 19.11.19 um 14:47 schrieb Benjamin Gaignard:
> >>>> When compiling with W=1 few warnings about unused variables show up.
> >>>> This patch removes all the involved variables.
> >>>>
> >>>> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...com>
> >>>> ---
> >>>> drivers/gpu/drm/drm_modes.c | 22 +++-------------------
> >>>> 1 file changed, 3 insertions(+), 19 deletions(-)
> >>>>
> >>>> diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
> >>>> index 88232698d7a0..aca901aff042 100644
> >>>> --- a/drivers/gpu/drm/drm_modes.c
> >>>> +++ b/drivers/gpu/drm/drm_modes.c
> >>>> @@ -233,7 +233,7 @@ struct drm_display_mode *drm_cvt_mode(struct drm_device *dev, int hdisplay,
> >>>> /* 3) Nominal HSync width (% of line period) - default 8 */
> >>>> #define CVT_HSYNC_PERCENTAGE 8
> >>>> unsigned int hblank_percentage;
> >>>> - int vsyncandback_porch, vback_porch, hblank;
> >>>> + int vsyncandback_porch, hblank;
> >>>>
> >>>> /* estimated the horizontal period */
> >>>> tmp1 = HV_FACTOR * 1000000 -
> >>>> @@ -249,7 +249,6 @@ struct drm_display_mode *drm_cvt_mode(struct drm_device *dev, int hdisplay,
> >>>> else
> >>>> vsyncandback_porch = tmp1;
> >>>> /* 10. Find number of lines in back porch */
> >>>> - vback_porch = vsyncandback_porch - vsync;
> >>>> drm_mode->vtotal = vdisplay_rnd + 2 * vmargin +
> >>>> vsyncandback_porch + CVT_MIN_V_PORCH;
> >>>> /* 5) Definition of Horizontal blanking time limitation */
> >>>> @@ -386,9 +385,8 @@ drm_gtf_mode_complex(struct drm_device *dev, int hdisplay, int vdisplay,
> >>>> int top_margin, bottom_margin;
> >>>> int interlace;
> >>>> unsigned int hfreq_est;
> >>>> - int vsync_plus_bp, vback_porch;
> >>>> - unsigned int vtotal_lines, vfieldrate_est, hperiod;
> >>>> - unsigned int vfield_rate, vframe_rate;
> >>>> + int vsync_plus_bp;
> >>>> + unsigned int vtotal_lines;
> >>>> int left_margin, right_margin;
> >>>> unsigned int total_active_pixels, ideal_duty_cycle;
> >>>> unsigned int hblank, total_pixels, pixel_freq;
> >>>> @@ -451,23 +449,9 @@ drm_gtf_mode_complex(struct drm_device *dev, int hdisplay, int vdisplay,
> >>>> /* [V SYNC+BP] = RINT(([MIN VSYNC+BP] * hfreq_est / 1000000)) */
> >>>> vsync_plus_bp = MIN_VSYNC_PLUS_BP * hfreq_est / 1000;
> >>>> vsync_plus_bp = (vsync_plus_bp + 500) / 1000;
> >>>> - /* 9. Find the number of lines in V back porch alone: */
> >>>> - vback_porch = vsync_plus_bp - V_SYNC_RQD;
> >>>> /* 10. Find the total number of lines in Vertical field period: */
> >>>> vtotal_lines = vdisplay_rnd + top_margin + bottom_margin +
> >>>> vsync_plus_bp + GTF_MIN_V_PORCH;
> >>>> - /* 11. Estimate the Vertical field frequency: */
> >>>> - vfieldrate_est = hfreq_est / vtotal_lines;
> >>>> - /* 12. Find the actual horizontal period: */
> >>>> - hperiod = 1000000 / (vfieldrate_rqd * vtotal_lines);
> >>>> -
> >>>> - /* 13. Find the actual Vertical field frequency: */
> >>>> - vfield_rate = hfreq_est / vtotal_lines;
> >>>> - /* 14. Find the Vertical frame frequency: */
> >>>> - if (interlaced)
> >>>> - vframe_rate = vfield_rate / 2;
> >>>> - else
> >>>> - vframe_rate = vfield_rate;
> >>> The amount of unused code is quite large, which makes me wonder if
> >>> there's something missing below where these variables are supposed to be
> >>> used.
> >>>
> >>> If these variables can be removed, comments should mention that steps 9
> >>> and 11 to 14 are being left out. After all, the function is fairly
> >>> explicit about implementing the GTF algorithm step by step.
> >>>
> >>> Best regards
> >>> Thomas
> >> If the goal is to keep all the steps then I could prefix all problematic
> >> variables with __maybe_unused macro.
> > The effect is the same; it hides a potential bug that should be analyzed
> > and fixed. If you have the time, please look at the code and figure out
> > what it's supposed to do, and why isn't it using the information. Look
> > at git blame and log, was it always so, or did something change?
> >
> > The warnings are about potential bugs. The objective or end goal is to
> > fix the bugs, not to silence the warnings.
> This code haven't change since it has been added by commit:
> 26bbdadad356e ("drm/mode: add the GTF algorithm in kernel space")
> The variables that I'm removing are not used anywhere else.
> The algorithm is copy from xserver/hw/xfree86/modes/xf86gtf.c where
> vframe_rate and v_back_porch are used with (void) calls:
> (void) v_back_porch;
> (void) v_frame_rate;
> It is another way avoid the warnings.
> Note that if you start removing v_frame_rate then vfield_rate becomes
> unused, etc...
I'd say we should do the same thing then as xf86 and just mark them up as
unused. Might be good to double-check with the spec at least whether
they're really not unused, or whether we have some issue. But given that
it seems to have worked for ages, I suspect it's all good.
Removing the code otoh feels a bit icky.
-Daniel
>
> Benjamin
>
> >
> > BR,
> > Jani.
> >
> >
> >> Benjamin
> >>
> >>>> /* 15. Find number of pixels in left margin: */
> >>>> if (margins)
> >>>> left_margin = (hdisplay_rnd * GTF_MARGIN_PERCENTAGE + 500) /
> >>>>
> >> _______________________________________________
> >> dri-devel mailing list
> >> dri-devel@...ts.freedesktop.org
> >> https://lists.freedesktop.org/mailman/listinfo/dri-devel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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