linux-kernel - Re: [PATCH v2 01/13] drm/bridge: samsung-dsim: separate LINK and DPHY status registers

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Message-ID: <922117777d718b77c86be3a43e86dd7f@disroot.org>
Date: Fri, 27 Jun 2025 12:29:01 +0000
From: Kaustabh Chakraborty <kauschluss@...root.org>
To: Inki Dae <daeinki@...il.com>
Cc: Jagan Teki <jagan@...rulasolutions.com>, Marek Szyprowski
 <m.szyprowski@...sung.com>, Andrzej Hajda <andrzej.hajda@...el.com>, Neil
 Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>,
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>, Jonas Karlman
 <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, Maarten
 Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard
 <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, David Airlie
 <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, Rob Herring
 <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Seung-Woo Kim <sw0312.kim@...sung.com>, Kyungmin Park
 <kyungmin.park@...sung.com>, Krzysztof Kozlowski <krzk@...nel.org>, Alim
 Akhtar <alim.akhtar@...sung.com>, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-samsung-soc@...r.kernel.org
Subject: Re: [PATCH v2 01/13] drm/bridge: samsung-dsim: separate LINK and DPHY
 status registers

On 2025-06-27 10:07, Inki Dae wrote:
> 2025년 6월 27일 (금) 오전 4:42, Kaustabh Chakraborty 
> <kauschluss@...root.org>님이 작성:
>> 
>> Exynos7870's DSIM has separate registers for LINK and DPHY status. 
>> This
>> is in contrast to other devices in the driver which use a single
>> register for both.
>> 
>> Add their respective entries in the register list. Devices having a
>> single status register have been assigned the same offset for both
>> entries.
>> 
>> Signed-off-by: Kaustabh Chakraborty <kauschluss@...root.org>
>> ---
>>  drivers/gpu/drm/bridge/samsung-dsim.c | 15 +++++++++------
>>  1 file changed, 9 insertions(+), 6 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c 
>> b/drivers/gpu/drm/bridge/samsung-dsim.c
>> index 
>> f2f666b27d2d5ec016d7a7f47c87fcdf1377d41a..7fd4c34cdc3170d363942f98feec048097da3c06 
>> 100644
>> --- a/drivers/gpu/drm/bridge/samsung-dsim.c
>> +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
>> @@ -30,7 +30,7 @@
>>  /* returns true iff both arguments logically differs */
>>  #define NEQV(a, b) (!(a) ^ !(b))
>> 
>> -/* DSIM_STATUS */
>> +/* DSIM_DPHY_STATUS */
>>  #define DSIM_STOP_STATE_DAT(x)         (((x) & 0xf) << 0)
>>  #define DSIM_STOP_STATE_CLK            BIT(8)
>>  #define DSIM_TX_READY_HS_CLK           BIT(10)
>> @@ -239,7 +239,8 @@ enum samsung_dsim_transfer_type {
>>  };
>> 
>>  enum reg_idx {
>> -       DSIM_STATUS_REG,        /* Status register */
> 
> According to the datasheets I have, both Exynos5422 and Exynos7420 use
> DSIM_STATUS, while Exynos8890 splits this into DSIM_LINK_STATUS and
> DSIM_PHY_STATUS. It appears that Exynos7870 follows the same approach
> as Exynos8890.
> 
> The current modification removes the legacy DSIM_STATUS_REG and adds
> new DSIM_LINK_STATUS_REG and DSIM_DPHY_STATUS_REG. However, this
> change causes the register names used for older SoC versions to differ
> from those in the datasheets, so I think it is better to keep the
> legacy name for backward compatibility.
> 
> How about modifying it as follows?
> enum reg_idx {
>     DSIM_STATUS_REG,          /* Status register (legacy) */
>     DSIM_LINK_STATUS_REG,     /* Link status register (Exynos7870, ...) 
> */
>     DSIM_PHY_STATUS_REG,      /* PHY status register (Exynos7870, ...) 
> */
>     ...
> };
> 
> static const unsigned int exynos7870_reg_ofs[] = {
>     [DSIM_STATUS_REG] = 0x00,        /* Legacy compatibility - use
> LINK_STATUS */
>     [DSIM_LINK_STATUS_REG] = 0x04,   /* Link status register */
>     [DSIM_PHY_STATUS_REG] = 0x08,    /* PHY status register */
>     ...
> };
> 
> Additionally, by configuring the hw_type field in the
> samsung_dsim_plat_data structure like you did with the patch[1], you
> can use the appropriate register name for each SoC as shown below:
> if (dsi->plat_data->hw_type == DSIM_TYPE_EXYNOS7870)

I've instead added a flag to the driver data indicating the
availability of legacy status register. In my opinion, this
approach quickly turns cumbersome as the number of variants
increase.

Thanks for the suggestion.

>     reg = samsung_dsim_read(dsi, DSIM_LINK_STATUS_REG);
> else
>     reg = samsung_dsim_read(dsi, DSIM_STATUS_REG);
> 
> 
> [1] [PATCH v2 12/13] drm/bridge: samsung-dsim: add driver support for
> exynos7870 DSIM bridge
> 
> Thanks,
> Inki Dae