[linux-sunxi] Re: [PATCH v4 08/26] drm/sun4i: sun6i_mipi_dsi: Fix VBP size calculation

[Jagan Teki]

On 20/11/18 9:55 PM, Jagan Teki wrote:
> On Tue, Nov 20, 2018 at 9:27 PM Maxime Ripard <maxime.ripard at bootlin.com> wrote:
>>
>> On Thu, Nov 15, 2018 at 11:19:53PM +0530, Jagan Teki wrote:
>>> On Thu, Nov 15, 2018 at 3:26 PM Maxime Ripard <maxime.ripard at bootlin.com> wrote:
>>>>
>>>> Hi,
>>>>
>>>> On Tue, Nov 13, 2018 at 04:46:15PM +0530, Jagan Teki wrote:
>>>>> The horizontal and vertical back porch calculation in BSP
>>>>> code is simply following the Linux drm comment diagram, in
>>>>> include/drm/drm_modes.h which is
>>>>>
>>>>> [hv]back porch = [hv]total - [hv]sync_end
>>>>>
>>>>> BSP code form BPI-M64-bsp is calculating vertical back porch as
>>>>> (from linux-sunxi/drivers/video/sunxi/disp2/disp/de/disp_lcd.c)
>>>>>
>>>>> timmings->ver_sync_time= panel_info->lcd_vspw;
>>>>> timmings->ver_back_porch= panel_info->lcd_vbp-panel_info->lcd_vspw;
>>>>>
>>>>> vbp = panel->lcd_vbp;
>>>>> vspw = panel->lcd_vspw;
>>>>> dsi_dev[sel]->dsi_basic_size0.bits.vbp = vbp-vspw;
>>>>> dsi_dev[sel]->dsi_basic_size0.bits.vbp = panel->lcd_vbp - panel->lcd_vspw;
>>>>> =>  timmings->ver_back_porch + panel_info->lcd_vspw - panel_info->lcd_vspw
>>>>> =>  timmings->ver_back_porch
>>>>> =>  mode->vtotal - mode->end
>>>>>
>>>>> Which evatually same as mode->vtotal - mode->vsync_end so update the
>>>>> same in SUN6I_DSI_BASIC_SIZE0_VBP
>>>>>
>>>>> On the information note, existing SUN6I_DSI_BASIC_SIZE0_VSA is proper
>>>>> value.
>>>>>
>>>>> Signed-off-by: Jagan Teki <jagan at amarulasolutions.com>
>>>>
>>>> I've tested your changes on my A33 board, and this commit will break
>>>> it.
>>>>
>>>> It creates vblank timeouts, and visual artifacts at the bottom of the
>>>> display.
>>>
>>> Strange, VBP is earlier gives front porch which is anyway wrong.
>>>
>>>>
>>>> Later commits seem to fix the issue, but will create some blanking on
>>>> the upper third of the display.
>>>>
>>>> Since the documentation is quite sparse, and a MIPI-DSI analyzer is
>>>> way too expensive, I'd really like to have at least what each of these
>>>> commits are actually fixing, and what symptoms each of these were
>>>> causing, and not just "the BSP does it".
>>>
>>> W/o this 2-lane panel is breaking, same vblank timeout and visual
>>> artifacts at the bottom of the panel. though the commits may reference
>>> BSP, I have at-least tested on 3 different panels for us to prove its
>>> working.
>>>
>>>> Having some datasheet for the panels you had working would help too.
>>>
>>> Unfortunately datasheet doesn't have any required information what we
>>> actually looking for.
>>
>> Not even the timings? How did you get that information then?
> 
> datasheet has timing values, but this changes need controller
> information about VBP register that I don't have. But again existing
> VBP is not back porch for real, it's front porch.
> 

I'm about to send next version by combining with burst mode changes in
one series. Do you have any further inputs on this. I didn't not see
any breakage with 4-lane devices, but has issue with 2-lane w/o this change.