Re: [PATCH v1 3/3] drm/stm: Add STM32 DSI host driver

[Archit Taneja <architt@codeaurora.org>]

Hi,

On 05/15/2017 04:03 PM, Philippe CORNU wrote:
> Hi Neil,
> Many thanks for your comments.
>
> The PHY part of the MIPI DSI is the main difference between all chipsets
> based on the Synopsys DesignWare MIPI DSI.
> There is no "generic DSI PHY interface" and that is probably why all soc
> vendors have implemented their own drivers (RockChip, NXP/Freescale,
> HiSilicon and now STM32).

We don't really need a generic DSI PHY interface to ensure we use a common
bridge driver. We need to do what's been done in the DW HDMI bridge driver.
The dw_hdmi_plat_data struct contains phy ops, which can be used to abstract
vendor PHYs.

>
> Regarding creating a "generic dw MIPI DSI bridge" as the recent dw hdmi
> bridge, several attempts have been done in the past but without success:
> * Liu Ying from Freescale in February 2015
> (https://lkml.org/lkml/2015/2/12/38).
> * Chris Zhong from Rockchip in November 2015
> (http://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1024586.html).

We can't have 3 almost identical DW MIPI DSI implementations in the kernel.
You'll need to separate out the vendor specific PHY pieces into ops (like
it's done in the DW HDMI) and post a bridge driver for this.

You don't need to convert the existing rockhip and hisilicon implementations
into bridge drivers. We can CC the authors of the rockchip and hisil so that
they can adapt to the bridge driver too.

Thanks,
Archit

>
> The Rockchip driver looks nice and is updated regularly.
> So, instead of creating a new driver for the STM32 family, we decided to
> use Rockchip’s in our own drm/stm directory and replace the
> Rockchip-specific PHY by the STM32.
>
> Comments are welcome :-)
> Many thanks,
> Philippe
>
>
> On 05/15/2017 10:22 AM, Neil Armstrong wrote:
>> On 05/12/2017 04:56 PM, Philippe CORNU wrote:
>>> This mipi dsi host driver is based on the Rockchip version of the
>>> Synopsys Designware mipi dsi driver (rockchip/dw-mipi-dsi.c)
>>> modified for the stm32 family:
>>> - replace Rockchip digital & phy specific extensions with stm32's ones.
>>> - add a bridge
>>>
>>> Signed-off-by: Philippe CORNU <philippe.cornu@st.com>
>>> ---
>>>  drivers/gpu/drm/stm/Kconfig       |    7 +
>>>  drivers/gpu/drm/stm/Makefile      |    2 +
>>>  drivers/gpu/drm/stm/dw-mipi-dsi.c | 1197 +++++++++++++++++++++++++++++++++++++
>>>  3 files changed, 1206 insertions(+)
>>>  create mode 100644 drivers/gpu/drm/stm/dw-mipi-dsi.c
>>>
>>> diff --git a/drivers/gpu/drm/stm/Kconfig b/drivers/gpu/drm/stm/Kconfig
>>> index 2c4817f..0007789 100644
>>> --- a/drivers/gpu/drm/stm/Kconfig
>>> +++ b/drivers/gpu/drm/stm/Kconfig
>>> @@ -14,3 +14,10 @@ config DRM_STM
>>>  	  STMicroelectronics STM32 MCUs.
>>>  	  To compile this driver as a module, choose M here: the module
>>>  	  will be called stm-drm.
>>> +
>>> +config DRM_STM_DSI
>>> +	tristate "MIPI DSI support for STMicroelectronics SoC"
>>> +	depends on DRM_STM
>>> +	select DRM_MIPI_DSI
>>> +	help
>>> +	  Choose this option for MIPI DSI support on STMicroelectronics SoC.
>>> diff --git a/drivers/gpu/drm/stm/Makefile b/drivers/gpu/drm/stm/Makefile
>>> index e114d45..e448a93 100644
>>> --- a/drivers/gpu/drm/stm/Makefile
>>> +++ b/drivers/gpu/drm/stm/Makefile
>>> @@ -4,4 +4,6 @@ stm-drm-y := \
>>>  	drv.o \
>>>  	ltdc.o
>>>
>>> +obj-$(CONFIG_DRM_STM_DSI) += dw-mipi-dsi.o
>>> +
>>>  obj-$(CONFIG_DRM_STM) += stm-drm.o
>>> diff --git a/drivers/gpu/drm/stm/dw-mipi-dsi.c b/drivers/gpu/drm/stm/dw-mipi-dsi.c
>>> new file mode 100644
>>> index 0000000..4b7f7b9
>>> --- /dev/null
>>> +++ b/drivers/gpu/drm/stm/dw-mipi-dsi.c
>>
>>
>> Hi Philippe,
>>
>> First question, why couldn't this be transformed as a bridge driver along the Synopsys DW-HDMI driver ?
>>
>> Neil
>>
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