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Message-ID: <88e53197-2819-c068-eba6-a218a19d8d15@denx.de>
Date:   Mon, 17 Apr 2023 22:07:56 +0200
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Subject: Re: [PATCH 5/6] drm: bridge: samsung-dsim: Support non-burst mode
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To:     Adam Ford <aford173@gmail.com>
Cc:     dri-devel@lists.freedesktop.org, m.szyprowski@samsung.com,
        aford@beaconembedded.com, Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Shawn Guo <shawnguo@kernel.org>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        Pengutronix Kernel Team <kernel@pengutronix.de>,
        Fabio Estevam <festevam@gmail.com>,
        NXP Linux Team <linux-imx@nxp.com>,
        Inki Dae <inki.dae@samsung.com>,
        Jagan Teki <jagan@amarulasolutions.com>,
        Andrzej Hajda <andrzej.hajda@intel.com>,
        Neil Armstrong <neil.armstrong@linaro.org>,
        Robert Foss <rfoss@kernel.org>,
        Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        Jonas Karlman <jonas@kwiboo.se>,
        Jernej Skrabec <jernej.skrabec@gmail.com>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Frieder Schrempf <frieder.schrempf@kontron.de>,
        devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, Lucas Stach <l.stach@pengutronix.de>
References: <20230415104104.5537-1-aford173@gmail.com>
 <20230415104104.5537-5-aford173@gmail.com>
 <807aa6c6-bbea-abcc-172d-17e22d1a3988@denx.de>
 <CAHCN7x+NUnMtLbj_7A_uqxPsi5NXRXsPFwDnn=sf1bgm-Q-BsQ@mail.gmail.com>
From:   Marek Vasut <marex@denx.de>
In-Reply-To: <CAHCN7x+NUnMtLbj_7A_uqxPsi5NXRXsPFwDnn=sf1bgm-Q-BsQ@mail.gmail.com>
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On 4/17/23 13:57, Adam Ford wrote:
> On Sun, Apr 16, 2023 at 5:13 PM Marek Vasut <marex@denx.de> wrote:
>>
>> On 4/15/23 12:41, Adam Ford wrote:
>>> The high-speed clock is hard-coded to the burst-clock
>>> frequency specified in the device tree.  However, when
>>> using devices like certain bridge chips without burst mode
>>> and varying resolutions and refresh rates, it may be
>>> necessary to set the high-speed clock dynamically based
>>> on the desired pixel clock for the connected device.
>>
>> The link rate negotiation should happen internally between the nearest
>> bridge and DSIM, so please add that to DRM core instead of hacking
>> around it by tweaking the HS clock again.
> 
> I thought you tried to add something like this before and had some resistance.

Yes, all my attempts were rejected by a single reviewer. I suspended my 
efforts in that area for now.

> The Pixel clock is set by the bridge already without any new code
> added to the DRM core..  I am just reading that value that's there,
> and setting the clock accordingly.  I don't see how this is a hack.

Assume you have a DSI-to-HDMI bridge attached to your DSIM bridge, it 
operates in non-burst mode, like ADV7533 . How would you configure the 
HS clock rate for such a bridge in DT ? (hint: you cannot, because the 
required clock comes from the EDID, which may not be available just yet)