From mboxrd@z Thu Jan 1 00:00:00 1970 From: Laurent Pinchart Subject: Re: [PATCH v2 1/8] drm/bridge: use bus flags in bridge timings Date: Fri, 14 Sep 2018 12:23:52 +0300 Message-ID: <6714863.eJMplaj6yU@avalon> References: <20180912183222.25414-1-stefan@agner.ch> <20180912183222.25414-2-stefan@agner.ch> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: In-Reply-To: <20180912183222.25414-2-stefan@agner.ch> Sender: linux-kernel-owner@vger.kernel.org To: Stefan Agner Cc: linus.walleij@linaro.org, airlied@linux.ie, robh+dt@kernel.org, mark.rutland@arm.com, shawnguo@kernel.org, s.hauer@pengutronix.de, p.zabel@pengutronix.de, kernel@pengutronix.de, fabio.estevam@nxp.com, linux-imx@nxp.com, architt@codeaurora.org, a.hajda@samsung.com, gustavo@padovan.org, maarten.lankhorst@linux.intel.com, sean@poorly.run, marcel.ziswiler@toradex.com, max.krummenacher@toradex.com, dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org List-Id: devicetree@vger.kernel.org Hi Stefan, Thankk you for the patch. On Wednesday, 12 September 2018 21:32:15 EEST Stefan Agner wrote: > The DRM bus flags conveys additional information on pixel data on > the bus. All currently available bus flags might be of interest for > a bridge. In the case at hand a dumb VGA bridge needs a specific > data enable polarity (DRM_BUS_FLAG_DE_LOW). > > Replace the sampling_edge field with input_bus_flags and allow all > currently documented bus flags. > > This changes the perspective from sampling side to the driving > side for the currently supported flags. We assume that the sampling > edge is always the opposite of the driving edge (hence we need to > invert the DRM_BUS_FLAG_PIXDATA_[POS|NEG]EDGE flags). This is an > assumption we already make for displays. For all we know it is a > safe assumption for bridges too. Please don't, that will get confusing very quickly. Flag names such as DRM_BUS_FLAG_PIXDATA_NEGEDGE don't mention sampling or driving. There's only a small comment next to their definition, which will easily be overlooked. I'd rather update the definition to cover both sampling and driving, and document the input_bus_flags field to explain that all flags refer to sampling. > Signed-off-by: Stefan Agner > --- > drivers/gpu/drm/bridge/dumb-vga-dac.c | 6 +++--- > include/drm/drm_bridge.h | 11 +++++------ > 2 files changed, 8 insertions(+), 9 deletions(-) > > diff --git a/drivers/gpu/drm/bridge/dumb-vga-dac.c > b/drivers/gpu/drm/bridge/dumb-vga-dac.c index 9b706789a341..d5aa0f931ef2 > 100644 > --- a/drivers/gpu/drm/bridge/dumb-vga-dac.c > +++ b/drivers/gpu/drm/bridge/dumb-vga-dac.c > @@ -234,7 +234,7 @@ static int dumb_vga_remove(struct platform_device *pdev) > */ > static const struct drm_bridge_timings default_dac_timings = { > /* Timing specifications, datasheet page 7 */ > - .sampling_edge = DRM_BUS_FLAG_PIXDATA_POSEDGE, > + .input_bus_flags = DRM_BUS_FLAG_PIXDATA_NEGEDGE, > .setup_time_ps = 500, > .hold_time_ps = 1500, > }; > @@ -245,7 +245,7 @@ static const struct drm_bridge_timings > default_dac_timings = { */ > static const struct drm_bridge_timings ti_ths8134_dac_timings = { > /* From timing diagram, datasheet page 9 */ > - .sampling_edge = DRM_BUS_FLAG_PIXDATA_POSEDGE, > + .input_bus_flags = DRM_BUS_FLAG_PIXDATA_NEGEDGE, > /* From datasheet, page 12 */ > .setup_time_ps = 3000, > /* I guess this means latched input */ > @@ -258,7 +258,7 @@ static const struct drm_bridge_timings > ti_ths8134_dac_timings = { */ > static const struct drm_bridge_timings ti_ths8135_dac_timings = { > /* From timing diagram, datasheet page 14 */ > - .sampling_edge = DRM_BUS_FLAG_PIXDATA_POSEDGE, > + .input_bus_flags = DRM_BUS_FLAG_PIXDATA_NEGEDGE, > /* From datasheet, page 16 */ > .setup_time_ps = 2000, > .hold_time_ps = 500, > diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h > index bd850747ce54..45e90f4b46c3 100644 > --- a/include/drm/drm_bridge.h > +++ b/include/drm/drm_bridge.h > @@ -244,14 +244,13 @@ struct drm_bridge_funcs { > */ > struct drm_bridge_timings { > /** > - * @sampling_edge: > + * @input_bus_flags: > * > - * Tells whether the bridge samples the digital input signal > - * from the display engine on the positive or negative edge of the > - * clock, this should reuse the DRM_BUS_FLAG_PIXDATA_[POS|NEG]EDGE > - * bitwise flags from the DRM connector (bit 2 and 3 valid). > + * Additional settings this bridge requires for the pixel data on > + * the input bus (e.g. pixel signal polarity). See also > + * &drm_display_info->bus_flags. > */ > - u32 sampling_edge; > + u32 input_bus_flags; > /** > * @setup_time_ps: > * -- Regards, Laurent Pinchart