linux-kernel - Re: [PATCH 9/9] [DO NOT MERGE] drm/sun4i: rgb: Add 5% tolerance to dot clock frequency check

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Date:   Sat, 2 Feb 2019 17:32:42 -0800
From:   Vasily Khoruzhick <anarsoul@...il.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Maxime Ripard <maxime.ripard@...tlin.com>,
        devicetree <devicetree@...r.kernel.org>,
        Dave Airlie <airlied@...ux.ie>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>,
        Rob Herring <robh+dt@...nel.org>,
        Daniel Vetter <daniel@...ll.ch>, Chen-Yu Tsai <wens@...e.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Icenowy Zheng <icenowy@...c.io>
Subject: Re: [PATCH 9/9] [DO NOT MERGE] drm/sun4i: rgb: Add 5% tolerance to
 dot clock frequency check

On Thu, Oct 18, 2018 at 4:31 AM Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:

> 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.

Clock tolerance is not specified in ANX6345 datasheet.

> 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 ?

This particular platform requires ~1% deviation.

E.g. on Pinebook with 768p panel: requested clock: 73.0 MHz, real
clock: 72.296296 MHz (0.96%)
on Pinebook with 1080p panel: requested clock: 138.5 MHz, real clock:
138.461538 MHz (0.03%)

So unfortunately 0.5% is not enough.

Regards,
Vasily