Re: [PATCH 3/3] drm/bridge: ti-sn65dsi83: add test pattern generation support

[Maxime Ripard <mripard@kernel.org>]

[-- Attachment #1: Type: text/plain, Size: 1945 bytes --]

On Fri, Feb 27, 2026 at 11:41:29AM +0100, Marek Vasut wrote:
> On 2/26/26 5:16 PM, Luca Ceresoli wrote:
> > Generation of a test pattern output is a useful tool for panel bringup and
> > debugging, and very simple to support with this chip.
> > 
> > The value of REG_VID_CHA_ACTIVE_LINE_LENGTH_LOW needs to be divided by two
> > for the test pattern to work in dual LVDS mode. While not clearly stated in
> > the datasheet, this is needed according to the DSI Tuner [0] output. And
> > some dual-LVDS panels refuse to show any picture without this division by
> > two.
> > 
> > [0] https://www.ti.com/tool/DSI-TUNER
> > 
> > Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
> > ---
> >   drivers/gpu/drm/bridge/ti-sn65dsi83.c | 13 +++++++++++--
> >   1 file changed, 11 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi83.c b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> > index 17a885244e1e..ddc8b5e1dd15 100644
> > --- a/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> > +++ b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> > @@ -114,6 +114,7 @@
> >   #define REG_VID_CHA_HORIZONTAL_FRONT_PORCH	0x38
> >   #define REG_VID_CHA_VERTICAL_FRONT_PORCH	0x3a
> >   #define REG_VID_CHA_TEST_PATTERN		0x3c
> > +#define  REG_VID_CHA_TEST_PATTERN_EN		BIT(4)
> >   /* IRQ registers */
> >   #define REG_IRQ_GLOBAL				0xe0
> >   #define  REG_IRQ_GLOBAL_IRQ_EN			BIT(0)
> > @@ -134,6 +135,9 @@
> >   #define  REG_IRQ_STAT_CHA_SOT_BIT_ERR		BIT(2)
> >   #define  REG_IRQ_STAT_CHA_PLL_UNLOCK		BIT(0)
> > +static bool sn65dsi83_test_pattern;
> > +module_param_named(test_pattern, sn65dsi83_test_pattern, bool, 0644);
>
> Can this be enabled/disabled at runtime via sysfs attribute instead ?

Then you would have to deal with concurrency with the atomic state
updates, and it would really be better implemented as a connector
property.

In other words, it's probably enough for now :)

Maxime

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 273 bytes --]