From: laurent.pinchart@ideasonboard.com (Laurent Pinchart)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 9/9] [DO NOT MERGE] drm/sun4i: rgb: Add 5% tolerance to dot clock frequency check
Date: Thu, 18 Oct 2018 14:31:01 +0300 [thread overview]
Message-ID: <1585874.9P5eR8PMbl@avalon> (raw)
In-Reply-To: <20181018094258.oahlopafvm2udvoe@flea>
Hello,
On Thursday, 18 October 2018 12:42:58 EEST Maxime Ripard wrote:
> On Thu, Oct 18, 2018 at 11:18:06AM +0200, Daniel Vetter wrote:
> > On Thu, Oct 18, 2018 at 10:55 AM Laurent Pinchart wrote:
> >> On Thursday, 18 October 2018 10:33:27 EEST Icenowy Zheng wrote:
> >>> From: Chen-Yu Tsai <wens@csie.org>
> >>>
> >>> The panels shipped with Allwinner devices are very "generic", i.e.
> >>> they do not have model numbers or reliable sources of information
> >>> for the timings (that we know of) other than the fex files shipped
> >>> on them. The dot clock frequency provided in the fex files have all
> >>> been rounded to the nearest MHz, as that is the unit used in them.
> >>>
> >>> We were using the simple panel "urt,umsh-8596md-t" as a substitute
> >>> for the A13 Q8 tablets in the absence of a specific model for what
> >>> may be many different but otherwise timing compatible panels. This
> >>> was usable without any visual artifacts or side effects, until the
> >>> dot clock rate check was added in commit bb43d40d7c83 ("drm/sun4i:
> >>> rgb: Validate the clock rate").
> >>>
> >>> The reason this check fails is because the dotclock frequency for
> >>> this model is 33.26 MHz, which is not achievable with our dot clock
> >>> hardware, and the rate returned by clk_round_rate deviates slightly,
> >>> causing the driver to reject the display mode.
> >>>
> >>> The LCD panels have some tolerance on the dot clock frequency, even
> >>> if it's not specified in their datasheets.
> >>>
> >>> This patch adds a 5% tolerence to the dot clock check.
> >>
> >> Why do you think this shouldn't be merged ?
> >
> > It pisses of a lot of people who really insist upon accurate timing.
>
> It's not just about accurate timings. That 5% is a made-up limit, that
> never have really been confirmed by looking at the typical tolerancies
> of panels.
>
> And while being to relaxed might make some panels work that are not
> working currently, it might also break some panels that currently work
> and won't now, and ideally, we should really be able to let those
> panels work if they can, and filter out resolutions if they can't.
>
> > I think a better fix would be to have a dotclock range in drm_panel,
> > and some magic to figure out which one of these we can actually
> > do. Then tell userspace that this is the mode is should
> > request. That way userspace knows what the actual dotclock/refresh
> > rate is, and the panel still works.
>
> It's not just about panels, but also bridges with EDID where the
> tolerancy is not exposed.
Given that the tolerance is a property of the panel or bridge, I agree with
Daniel that it should be implemented there, or at least in cooperation with
drm_panel and drm_bridge.
Semi-related information, I think the CEA and VESA standards allow a 0.5%
clock tolerance. What is the maximum clock frequency deviation required for
this platform ?
--
Regards,
Laurent Pinchart
next prev parent reply other threads:[~2018-10-18 11:31 UTC|newest]
Thread overview: 77+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-18 7:33 [PATCH 0/9] Analogix ANX6345 RGB-(e)DP bridge support Icenowy Zheng
2018-10-18 7:33 ` [PATCH 1/9] drm/bridge: move ANA78xx driver to analogix subdirectory Icenowy Zheng
2018-10-18 8:47 ` Laurent Pinchart
2018-10-18 7:33 ` [PATCH 2/9] drm/bridge: split some definitions of ANX78xx to dedicated headers Icenowy Zheng
2018-10-18 7:33 ` [PATCH 3/9] drm/bridge: extract some Analogix I2C DP common code Icenowy Zheng
2018-10-18 7:33 ` [PATCH 4/9] dt-bindings: Add ANX6345 DP/eDP transmitter binding Icenowy Zheng
2018-10-18 8:53 ` Laurent Pinchart
2018-10-18 10:00 ` Icenowy Zheng
2018-10-18 11:23 ` Laurent Pinchart
2018-10-18 12:40 ` Icenowy Zheng
2018-10-25 18:30 ` Rob Herring
2018-10-26 0:08 ` Icenowy Zheng
2018-10-18 7:33 ` [PATCH 5/9] drm/bridge: Add Analogix anx6345 support Icenowy Zheng
2018-10-18 7:33 ` [PATCH 6/9] arm64: allwinner: a64: add pinmux for RGB666 LCD Icenowy Zheng
2018-10-18 7:33 ` [PATCH 7/9] arm64: allwinner: a64: enable ANX6345 bridge on Pinebook Icenowy Zheng
2018-10-18 15:17 ` Vasily Khoruzhick
2018-10-19 5:50 ` Icenowy Zheng
2018-10-18 7:33 ` [PATCH 8/9] arm64: allwinner: a64: enable ANX6345 bridge on TERES-I Icenowy Zheng
2018-10-18 7:33 ` [PATCH 9/9] [DO NOT MERGE] drm/sun4i: rgb: Add 5% tolerance to dot clock frequency check Icenowy Zheng
2018-10-18 8:55 ` Laurent Pinchart
2018-10-18 9:18 ` Daniel Vetter
2018-10-18 9:42 ` Maxime Ripard
2018-10-18 11:31 ` Laurent Pinchart [this message]
2018-10-18 12:18 ` Maxime Ripard
2018-10-18 12:50 ` Icenowy Zheng
2018-10-18 13:07 ` Maxime Ripard
2018-10-18 13:57 ` Laurent Pinchart
2019-02-03 1:32 ` Vasily Khoruzhick
2018-10-29 2:20 ` [PATCH 0/9] Analogix ANX6345 RGB-(e)DP bridge support Vasily Khoruzhick
2019-02-04 12:22 ` Torsten Duwe
2019-02-04 20:21 ` Vasily Khoruzhick
2019-02-03 18:54 [PATCH RESEND v2 00/12] " Vasily Khoruzhick
2019-02-03 18:54 ` [PATCH RESEND v2 01/12] drm/bridge: move ANA78xx driver to analogix subdirectory Vasily Khoruzhick
2019-02-03 18:54 ` [PATCH RESEND v2 02/12] drm/bridge: split some definitions of ANX78xx to dedicated headers Vasily Khoruzhick
2019-02-03 18:54 ` [PATCH RESEND v2 03/12] drm/bridge: extract some Analogix I2C DP common code Vasily Khoruzhick
2019-02-03 18:54 ` [PATCH RESEND v2 04/12] dt-bindings: Add ANX6345 DP/eDP transmitter binding Vasily Khoruzhick
2019-02-03 18:54 ` [PATCH RESEND v2 05/12] drm/bridge: Add Analogix anx6345 support Vasily Khoruzhick
2019-02-05 13:19 ` Torsten Duwe
2019-02-03 18:54 ` [PATCH RESEND v2 06/12] drm/sun4i: rgb: Add 1% tolerance to dclk frequency check when bridge is connected Vasily Khoruzhick
2019-02-04 14:20 ` Maxime Ripard
2019-02-04 16:26 ` Vasily Khoruzhick
2019-02-04 16:28 ` Icenowy Zheng
2019-02-04 18:50 ` [linux-sunxi] " Vasily Khoruzhick
2019-02-05 15:41 ` Maxime Ripard
2019-02-05 17:49 ` Vasily Khoruzhick
2019-02-06 9:16 ` Maxime Ripard
2019-02-06 11:42 ` Thierry Reding
2019-02-03 18:54 ` [PATCH RESEND v2 07/12] drm/panel: simple: don't fail if we don't have panel desc Vasily Khoruzhick
2019-02-03 18:54 ` [PATCH RESEND v2 08/12] dt-bindings: add binding for generic eDP panel Vasily Khoruzhick
2019-02-04 7:43 ` Thierry Reding
2019-02-04 8:13 ` Vasily Khoruzhick
2019-02-04 8:23 ` Thierry Reding
2019-02-04 9:40 ` Daniel Vetter
2019-02-04 11:22 ` Thierry Reding
2019-02-04 15:59 ` Daniel Vetter
2019-02-04 16:22 ` Thierry Reding
2019-02-05 8:57 ` Daniel Vetter
2019-02-05 10:24 ` Thierry Reding
2019-02-05 16:36 ` Daniel Vetter
2019-02-14 19:51 ` Vasily Khoruzhick
2019-02-14 20:05 ` Vasily Khoruzhick
2019-02-14 20:38 ` Rob Herring
2019-02-14 20:54 ` Vasily Khoruzhick
2019-02-04 16:11 ` Vasily Khoruzhick
2019-02-04 16:27 ` Thierry Reding
2019-02-04 16:39 ` Rob Herring
2019-02-04 17:02 ` [linux-sunxi] " Vasily Khoruzhick
2019-02-04 16:27 ` Rob Herring
2019-02-04 16:56 ` Thierry Reding
2019-02-04 17:07 ` Vasily Khoruzhick
2019-02-04 20:23 ` Rob Herring
2019-02-04 20:26 ` Vasily Khoruzhick
2019-02-04 20:34 ` Rob Herring
2019-02-03 18:54 ` [PATCH RESEND v2 09/12] drm/panel: simple: add " Vasily Khoruzhick
2019-02-03 18:54 ` [PATCH RESEND v2 10/12] arm64: allwinner: a64: add pinmux for RGB666 LCD Vasily Khoruzhick
2019-02-03 18:55 ` [PATCH RESEND v2 11/12] arm64: allwinner: a64: enable LCD-related hardware for Pinebook Vasily Khoruzhick
2019-02-03 18:55 ` [PATCH RESEND v2 12/12] arm64: allwinner: a64: enable LCD-related hardware for TERES-I Vasily Khoruzhick
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