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Subject: Re: [PATCH] drm/modes: remove unused variables
To:     Benjamin Gaignard <benjamin.gaignard@st.com>,
        maarten.lankhorst@linux.intel.com, mripard@kernel.org,
        sean@poorly.run, airlied@linux.ie, daniel@ffwll.ch
Cc:     linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org
References: <20191119134706.10893-1-benjamin.gaignard@st.com>
From:   Thomas Zimmermann <tzimmermann@suse.de>
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Date:   Wed, 4 Dec 2019 10:35:50 +0100
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From: Thomas Zimmermann <tzimmermann@suse.de>
To: Benjamin Gaignard <benjamin.gaignard@st.com>,
 maarten.lankhorst@linux.intel.com, mripard@kernel.org, sean@poorly.run,
 airlied@linux.ie, daniel@ffwll.ch
Cc: linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org
Message-ID: <8056f838-3ebf-26db-f5be-3e78d61aa512@suse.de>
Subject: Re: [PATCH] drm/modes: remove unused variables
References: <20191119134706.10893-1-benjamin.gaignard@st.com>
In-Reply-To: <20191119134706.10893-1-benjamin.gaignard@st.com>

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Hi

Am 19.11.19 um 14:47 schrieb Benjamin Gaignard:
> When compiling with W=3D1 few warnings about unused variables show up.
> This patch removes all the involved variables.
>=20
> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com>
> ---
>  drivers/gpu/drm/drm_modes.c | 22 +++-------------------
>  1 file changed, 3 insertions(+), 19 deletions(-)
>=20
> 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_de=
vice *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;
> =20
>  		/* estimated the horizontal period */
>  		tmp1 =3D HV_FACTOR * 1000000  -
> @@ -249,7 +249,6 @@ struct drm_display_mode *drm_cvt_mode(struct drm_de=
vice *dev, int hdisplay,
>  		else
>  			vsyncandback_porch =3D tmp1;
>  		/* 10. Find number of lines in back porch */
> -		vback_porch =3D vsyncandback_porch - vsync;
>  		drm_mode->vtotal =3D 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 hd=
isplay, 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 h=
display, int vdisplay,
>  	/* [V SYNC+BP] =3D RINT(([MIN VSYNC+BP] * hfreq_est / 1000000)) */
>  	vsync_plus_bp =3D MIN_VSYNC_PLUS_BP * hfreq_est / 1000;
>  	vsync_plus_bp =3D (vsync_plus_bp + 500) / 1000;
> -	/*  9. Find the number of lines in V back porch alone: */
> -	vback_porch =3D vsync_plus_bp - V_SYNC_RQD;
>  	/*  10. Find the total number of lines in Vertical field period: */
>  	vtotal_lines =3D vdisplay_rnd + top_margin + bottom_margin +
>  			vsync_plus_bp + GTF_MIN_V_PORCH;
> -	/*  11. Estimate the Vertical field frequency: */
> -	vfieldrate_est =3D hfreq_est / vtotal_lines;
> -	/*  12. Find the actual horizontal period: */
> -	hperiod =3D 1000000 / (vfieldrate_rqd * vtotal_lines);
> -
> -	/*  13. Find the actual Vertical field frequency: */
> -	vfield_rate =3D hfreq_est / vtotal_lines;
> -	/*  14. Find the Vertical frame frequency: */
> -	if (interlaced)
> -		vframe_rate =3D vfield_rate / 2;
> -	else
> -		vframe_rate =3D 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

>  	/*  15. Find number of pixels in left margin: */
>  	if (margins)
>  		left_margin =3D (hdisplay_rnd * GTF_MARGIN_PERCENTAGE + 500) /
>=20

--=20
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 N=C3=BCrnberg, Germany
(HRB 36809, AG N=C3=BCrnberg)
Gesch=C3=A4ftsf=C3=BChrer: Felix Imend=C3=B6rffer


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