linux-kernel - Re: [linux-sunxi] Re: [PATCH 07/12] drm/sun4i: sun6i_mipi

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Date:   Wed, 3 Oct 2018 08:52:06 +0530
From:   Jagan Teki <jagan@...nedev.com>
To:     maxime.ripard@...tlin.com, Jagan Teki <jagan@...rulasolutions.com>
Cc:     Chen-Yu Tsai <wens@...e.org>, Icenowy Zheng <icenowy@...c.io>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Vasily Khoruzhick <anarsoul@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        David Airlie <airlied@...ux.ie>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        Michael Trimarchi <michael@...rulasolutions.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [linux-sunxi] Re: [PATCH 07/12] drm/sun4i: sun6i_mipi_dsi: Fix
 TCON DRQ set bits

On Tuesday 02 October 2018 06:50 PM, Maxime Ripard wrote:
> On Thu, Sep 27, 2018 at 11:15:50PM +0530, Jagan Teki wrote:
>> On Thu, Sep 27, 2018 at 10:28 PM Maxime Ripard
>> <maxime.ripard@...tlin.com> wrote:
>>>
>>> On Thu, Sep 27, 2018 at 05:18:45PM +0530, Jagan Teki wrote:
>>>> TCON DRQ set bits for non-burst DSI mode can computed via
>>>> horizontal front porch instead of front porch + sync timings.
>>>>
>>>> Since there no documentation for TCON_DRQ_REG(0x7c) register
>>>> this change is taken as reference from BPI-M64-bsp.
>>>
>>> Detailing more what the issue is would be great.
>>>
>>>> Signed-off-by: Jagan Teki <jagan@...rulasolutions.com>
>>>> ---
>>>>   drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 4 ++--
>>>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
>>>> index 599284971ab6..9918fdb990ff 100644
>>>> --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
>>>> +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
>>>> @@ -367,9 +367,9 @@ static void sun6i_dsi_setup_burst(struct sun6i_dsi *dsi,
>>>>        struct mipi_dsi_device *device = dsi->device;
>>>>        u32 val = 0;
>>>
>>> The computation here is in the A64 driver:
>>>
>>> if ((panel->lcd_ht - panel->lcd_x - panel->lcd_hbp) < 21) {
>>>          dsi_dev[sel]->dsi_tcon_drq.bits.drq_mode = 0;
>>> } else {
>>>          dsi_dev[sel]->dsi_tcon_drq.bits.drq_set =
>>>                  (panel->lcd_ht-panel->lcd_x-panel->lcd_hbp-20) *
>>>                  dsi_pixel_bits[panel->lcd_dsi_format]/(8*4);
>>> }
>>>
>>> It is testing that the sync + front porch is smaller than 21, and
>>> otherwise sets the drq.
>>>
>>>> -     if ((mode->hsync_end - mode->hdisplay) > 20) {
>>>
>>> My code here is testing that the difference between hsync_end and
>>> hdisplay is superior to 20, and sets the DRQ if true. The condition is
>>> reversed, but otherwise, that difference is the front porch plus the
>>> sync length.
>>
>> True, I understand this, but does drq setting here is specific to SoC?
>> I thought of finding DRQ in A31 BSP but I couldn't find the code. do
>> you have bsp somewhere in github?
>>
>>>
>>>> +     if ((mode->hsync_start - mode->hdisplay) > 20) {
>>>
>>> However, you are testing for just the front porch, unlike what your
>>> commit log is saying, and unlike what allwinner's code is saying. So
>>> this deserves some explanation.
>>
>> but A64 is doing this, do you think it's completely A64 specific or
>> testing panel with front porch drq?
> 
> See the above code excerpt:
> panel->lcd_ht - panel->lcd_x - panel->lcd_hbp
> 
> This is hsync + front porch. Not the sole front porch. So no, it's not
> doing this.

=> panel->lcd_ht - panel->lcd_x - panel->lcd_hbp

from drivers/video/sunxi/disp2/disp/de/disp_lcd.c
timmings->hor_front_porch= panel_info->lcd_ht-panel_info->lcd_hbp - 
panel_info->lcd_x;

=> (timmings->hor_front_porch + panel->lcd_hbp + panel->lcd_x) - 
panel->lcd_x - panel->hbp
=> timmings->hor_front_porch
=> mode->hsync_start - mode->hdisplay

This is simply a front porch.