linux-kernel - Re: [PATCH v2] drm/meson: add mode selection limits against specific SoC revisions

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Date:   Wed, 29 Apr 2020 00:03:13 +0200
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Neil Armstrong <narmstrong@...libre.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drm/meson: add mode selection limits against specific
 SoC revisions

Hi Neil,

On Tue, Apr 28, 2020 at 11:21 AM Neil Armstrong <narmstrong@...libre.com> wrote:
>
> The Amlogic S805X/Y uses the same die as the S905X, but with more
> limited graphics capabilities.
>
> This adds a soc version detection adding specific limitations on the HDMI
> mode selections.
>
> Here, we limit to HDMI 1.3a max HDMI PHY clock frequency.
for my own education: 1.65GHz from the PLL will be divided down to 165MHz
isn't this more like the limit of HDMI 1.2a?

> Changes sinces v1:
> - Moved frequency check in the vclk code, and also checks DMT modes
>
> Signed-off-by: Neil Armstrong <narmstrong@...libre.com>
Acked-by: Martin Blumenstingl <martin.blumenstingl@...glemail.com>

This looks good to me based on the current limitations of meson_vclk.c
If we switch to CCF based VPU clock rate changes then we should do
this in the clock driver by calling clk_hw_set_rate_range(hdmi_pll, 0,
1.65GHz)

The good thing is: we can re-use struct meson_drm_soc_limits even
after switching to CCF.
We will just need to set the max PHY freq using
clk_round_rate(hdmi_pll, ULONG_MAX)


Martin