linux-kernel - Re: [PATCH v8 02/15] drm/sun4i: tcon: Compute DCLK dividers based on format, lanes

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Message-ID: <CAMty3ZCEjVhTvjUgvnkR7SpeC8m10f0FpnvLWCEkMksbhfWR2Q@mail.gmail.com>
Date:   Thu, 21 Mar 2019 19:41:28 +0530
From:   Jagan Teki <jagan@...rulasolutions.com>
To:     Sergey Suloev <ssuloev@...altech.com>
Cc:     Maxime Ripard <maxime.ripard@...tlin.com>,
        devicetree <devicetree@...r.kernel.org>,
        David Airlie <airlied@...ux.ie>,
        Michael Turquette <mturquette@...libre.com>,
        linux-sunxi <linux-sunxi@...glegroups.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Chen-Yu Tsai <wens@...e.org>, Rob Herring <robh+dt@...nel.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Michael Trimarchi <michael@...rulasolutions.com>,
        linux-amarula@...rulasolutions.com,
        linux-clk <linux-clk@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v8 02/15] drm/sun4i: tcon: Compute DCLK dividers based on
 format, lanes

Hi Sergey,

On Tue, Mar 19, 2019 at 5:47 PM Sergey Suloev <ssuloev@...altech.com> wrote:
>
> Hi, guys,
>
> On 3/19/19 1:53 PM, Maxime Ripard wrote:
>
> On Mon, Mar 11, 2019 at 09:36:27PM +0530, Jagan Teki wrote:
>
> On Mon, Mar 11, 2019 at 9:08 PM Maxime Ripard <maxime.ripard@...tlin.com> wrote:
>
> On Mon, Mar 11, 2019 at 07:06:24PM +0530, Jagan Teki wrote:
>
> pll-video => pll-mipi => tcon0 => tcon0-pixel-clock is the typical
> MIPI clock topology in Allwinner DSI controller.
>
> TCON dotclock driver is computing the desired DCLK divider based on
> panel pixel clock along with input DCLK min, max divider values from
> tcon driver and that would eventually set the pll-mipi clock rate.
>
> The current code allows the TCON clock divider to have a default 4
> for min, max ranges that would fail to compute the desired pll-mipi
> rate while supporting new panels.
>
> So, add the computation logic 'format/lanes' to dclk min and max dividers
> and instead of default 4. This computation logic align with Allwinner A64
> BSP, hoping that would work even for A33.
>
> Last time we discussed this, we found out that this wasn't the case,
> even in the BSP.
>
> This was the case for BSP to compute pll-mipi not for TCON_DSI clock
> register, SUN4I_TCON0_DCLK_REG, which marked the divider 4 by default.
>
> What compelling evidence have you found that makes you say otherwise?
>
> divider 4 isn't worked, this I would mentioned before as well.
>
> Maybe you mentionned it before, but it's nowhere to be found in your
> commit log.
>
> Tested this on 4 different panels, and below are the desired divider values
> and pll-mipi clock rate with respect to pixel clock frequency.
>
> - 55MHz pixel clock with 4-lane panel, and the desired DSI clock divider
>   is 6 with the output parent clock rate of 330MHz.
> - 30MHz pixel clock with 4-lane panel, and the desired DSI clock divider
>   is 6 with parent clock rate of 180MHz.
> - 27.5Mhz pixel clock with 2-lane pane, and the desired DSI clock divider
>   is 12 with the output parent clock rate of 330MHz.
> - 147MHz pixel clock with 4-lane panel, and the desired DSI clock divider
>   is 6 with the output parent clock rate of 882MHz.
>
> BSP trying to use this format/lane to compute dsi divider that in-turn
> using pll-mipi set_rate but TCON0_DCLK_REG keep constant 4.
>
> Feel free to reply to
> http://lists.infradead.org/pipermail/linux-arm-kernel/2019-February/629596.html
>
> And correct whatever is said there that isn't what is happening.
>
>
> excuse me if my message is out of topic.
>
> I just want let you know  that the code
>
> tcon->dclk_min_div = SUN6I_DSI_TCON_DIV;
> tcon->dclk_max_div = SUN6I_DSI_TCON_DIV;
>
> where SUN6I_DSI_TCON_DIV = 4  isn't working with my 2-lane panel: I am always getting the error:
>
>  [CRTC:38:crtc-0] vblank wait timed out
>
> As soon as I set
>
> tcon->dclk_min_div = tcon->dclk_max_div = bpp/lanes, i.e. 12
>
> the error disappears.

Yes, I did test the same in 2-lane panel. it worked with the logic.
thanks for testing.