linux-kernel - Re: [PATCH v5 19/22] drm/vc4: vec: Check for VEC output constraints

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Date:   Sun, 16 Oct 2022 20:12:48 +0200
From:   Mateusz Kwiatkowski <kfyatek@...il.com>
To:     Maxime Ripard <maxime@...no.tech>,
        Karol Herbst <kherbst@...hat.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        David Airlie <airlied@...ux.ie>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Lyude Paul <lyude@...hat.com>,
        Maxime Ripard <mripard@...nel.org>,
        Emma Anholt <emma@...olt.net>, Chen-Yu Tsai <wens@...e.org>,
        Samuel Holland <samuel@...lland.org>,
        Ben Skeggs <bskeggs@...hat.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Jernej Skrabec <jernej.skrabec@...il.com>
Cc:     Dom Cobley <dom@...pberrypi.com>, linux-sunxi@...ts.linux.dev,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Noralf Trønnes <noralf@...nnes.org>,
        intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        nouveau@...ts.freedesktop.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-arm-kernel@...ts.infradead.org,
        dri-devel@...ts.freedesktop.org,
        Hans de Goede <hdegoede@...hat.com>,
        Phil Elwell <phil@...pberrypi.com>
Subject: Re: [PATCH v5 19/22] drm/vc4: vec: Check for VEC output constraints

Hi Maxime,

W dniu 13.10.2022 o 15:19, Maxime Ripard pisze:
> From: Mateusz Kwiatkowski > > The VEC can accept pretty much any relatively reasonable mode, but still > has a bunch of constraints to meet. > > Let's create an atomic_check() implementation that will make sure we > don't end up accepting a non-functional mode. > > Acked-by: Noralf Trønnes > Signed-off-by: Mateusz Kwiatkowski > Signed-off-by: Maxime Ripard > --- > drivers/gpu/drm/vc4/vc4_vec.c | 48 +++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 48 insertions(+) > > diff --git a/drivers/gpu/drm/vc4/vc4_vec.c b/drivers/gpu/drm/vc4/vc4_vec.c > index 90e375a8a8f9..1fcb7baf874e 100644 > --- a/drivers/gpu/drm/vc4/vc4_vec.c > +++ b/drivers/gpu/drm/vc4/vc4_vec.c > @@ -453,6 +453,7 @@ static int vc4_vec_encoder_atomic_check(struct drm_encoder *encoder, > struct drm_crtc_state *crtc_state, > struct drm_connector_state *conn_state) > { > + const struct drm_display_mode *mode = &crtc_state->adjusted_mode; > const struct vc4_vec_tv_mode *vec_mode; > > vec_mode =
&vc4_vec_tv_modes[conn_state->tv.legacy_mode]; > @@ -461,6 +462,53 @@ static int vc4_vec_encoder_atomic_check(struct drm_encoder *encoder, > !drm_mode_equal(vec_mode->mode, &crtc_state->adjusted_mode)) > return -EINVAL; > > + if (mode->crtc_hdisplay % 4) > + return -EINVAL; > + > + if (!(mode->crtc_hsync_end - mode->crtc_hsync_start)) > + return -EINVAL; > + > + switch (mode->vtotal) { > + case 525: > + if (mode->crtc_vtotal > 262) > + return -EINVAL; > + > + if (mode->crtc_vdisplay < 1 || mode->crtc_vdisplay > 253) > + return -EINVAL; > + > + if (!(mode->crtc_vsync_start - mode->crtc_vdisplay)) > + return -EINVAL; > + > + if ((mode->crtc_vsync_end - mode->crtc_vsync_start) != 3) > + return -EINVAL; > + > + if ((mode->crtc_vtotal - mode->crtc_vsync_end) < 4) > + return -EINVAL; > + > + break; > + > + case 625: > + if (mode->crtc_vtotal > 312) > + return -EINVAL; > + > + if (mode->crtc_vdisplay < 1 || mode->crtc_vdisplay > 305) > + return -EINVAL; > + > + if
(!(mode->crtc_vsync_start - mode->crtc_vdisplay)) > + return -EINVAL; > + > + if ((mode->crtc_vsync_end - mode->crtc_vsync_start) != 3) > + return -EINVAL; > + > + if ((mode->crtc_vtotal - mode->crtc_vsync_end) < 2) > + return -EINVAL; > + > + break; > + > + default: > + return -EINVAL; > + } > + > return 0; > } In my original version of this function (https://github.com/raspberrypi/linux/pull/4406/files) the switch is over reference_mode->vtotal, not mode->vtotal. This was intended to explicitly allow a different value of mode->vtotal, to support non-standard modes, such as "fake" 525 lines with SECAM encoding, or the progressive modes. You're switching over mode->vtotal, which makes specifying those impossible. I don't think we should limit the users like that. We're removing reference_mode in patch 20/22, so adding a switch over reference_mode->vtotal is probably not a good idea -- in that case I'd switch over mode->htotal instead: 858 for "NTSC" and 864 for "PAL". This
may seem a bit weird, but any other value of htotal causes the VEC to output garbage anyway. Best regards, Mateusz Kwiatkowski