linux-kernel - Re: [PATCH] drm/modes: remove unused variables

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Message-ID: <f210413f-2d2f-9887-ca3b-a3c48564d9d6@st.com>
Date:   Wed, 4 Dec 2019 10:07:44 +0000
From:   Benjamin GAIGNARD <benjamin.gaignard@...com>
To:     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>
CC:     "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 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.

Benjamin

>
>>   	/*  15. Find number of pixels in left margin: */
>>   	if (margins)
>>   		left_margin = (hdisplay_rnd * GTF_MARGIN_PERCENTAGE + 500) /
>>