[PATCH V3 06/13] drm: bridge: icn6211: Add generic DSI-to-DPI PLL configuration

[Marek Vasut]

On 3/8/22 09:07, Jagan Teki wrote:
> On Fri, Mar 4, 2022 at 5:55 AM Marek Vasut <marex at denx.de> wrote:
>>
>> The chip contains fractional PLL, however the driver currently hard-codes
>> one specific PLL setting. Implement generic PLL parameter calculation code,
>> so any DPI panel with arbitrary pixel clock can be attached to this bridge.
>>
>> The datasheet for this bridge is not available, the PLL behavior has been
>> inferred from [1] and [2] and by analyzing the DPI pixel clock with scope.
>> The PLL limits might be wrong, but at least the calculated values match all
>> the example code available. This is better than one hard-coded pixel clock
>> value anyway.
>>
>> [1] https://github.com/rockchip-linux/kernel/blob/develop-4.19/drivers/gpu/drm/bridge/icn6211.c
>> [2] https://github.com/tdjastrzebski/ICN6211-Configurator
>>
>> Acked-by: Maxime Ripard <maxime at cerno.tech>
>> Signed-off-by: Marek Vasut <marex at denx.de>
>> Cc: Jagan Teki <jagan at amarulasolutions.com>
>> Cc: Maxime Ripard <maxime at cerno.tech>
>> Cc: Robert Foss <robert.foss at linaro.org>
>> Cc: Sam Ravnborg <sam at ravnborg.org>
>> Cc: Thomas Zimmermann <tzimmermann at suse.de>
>> To: dri-devel at lists.freedesktop.org
>> ---
>> V2: Rebase on next-20220214
>> V3: Add AB from Maxime
>> ---
>>   drivers/gpu/drm/bridge/chipone-icn6211.c | 87 +++++++++++++++++++++++-
>>   1 file changed, 84 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/bridge/chipone-icn6211.c b/drivers/gpu/drm/bridge/chipone-icn6211.c
>> index df8e75a068ad0..71c83a18984fa 100644
>> --- a/drivers/gpu/drm/bridge/chipone-icn6211.c
>> +++ b/drivers/gpu/drm/bridge/chipone-icn6211.c
>> @@ -163,6 +163,87 @@ static inline int chipone_dsi_write(struct chipone *icn,  const void *seq,
>>                  chipone_dsi_write(icn, d, ARRAY_SIZE(d));       \
>>          }
>>
>> +static void chipone_configure_pll(struct chipone *icn,
>> +                                 const struct drm_display_mode *mode)
>> +{
>> +       unsigned int best_p = 0, best_m = 0, best_s = 0;
>> +       unsigned int delta, min_delta = 0xffffffff;
>> +       unsigned int freq_p, freq_s, freq_out;
>> +       unsigned int p_min, p_max;
>> +       unsigned int p, m, s;
>> +       unsigned int fin;
>> +
>> +       /*
>> +        * DSI clock lane frequency (input into PLL) is calculated as:
>> +        *  DSI_CLK = mode clock * bpp / dsi_data_lanes / 2
>> +        * the 2 is there because the bus is DDR.
>> +        *
>> +        * DPI pixel clock frequency (output from PLL) is mode clock.
>> +        *
>> +        * The chip contains fractional PLL which works as follows:
>> +        *  DPI_CLK = ((DSI_CLK / P) * M) / S
>> +        * P is pre-divider, register PLL_REF_DIV[3:0] is 2^(n+1) divider
>> +        *                   register PLL_REF_DIV[4] is extra 1:2 divider
>> +        * M is integer multiplier, register PLL_INT(0) is multiplier
>> +        * S is post-divider, register PLL_REF_DIV[7:5] is 2^(n+1) divider
>> +        *
>> +        * It seems the PLL input clock after applying P pre-divider have
>> +        * to be lower than 20 MHz.
>> +        */
>> +       fin = mode->clock * mipi_dsi_pixel_format_to_bpp(icn->dsi->format) /
> 
> no dsi in chipone structure. please preserve format during the probe.
> 
> drivers/gpu/drm/bridge/chipone-icn6211.c:193:61: error: ‘struct
> chipone’ has no member named ‘dsi’
>    193 |         fin = mode->clock *
> mipi_dsi_pixel_format_to_bpp(icn->dsi->format) /

Ah , yes, this was added in
[PATCH V3 11/13] drm: bridge: icn6211: Add I2C configuration support
and needs to be moved here.