Re: [PATCH v6] drm/omap: dsi: avoid sending bta sync all the time in writes

[Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>]

Hi,

On 04/08/2026 11:37, Andreas Kemnade wrote:
> Some chips need configuration commands to be sent first, before they can
> send data. TC358762 for example needs PPI_LPTXTIMECNT configured
> and PPI_STARTPPI set to 1 to be able to transmit anything. To be able to
> configure such chips, do not send bta sync during writes if no acks are
> requested. Instead just wait for the packet to be sent to avoid FIFO
> overflows. There might be more to do about acks, but there seem to be
> virtually no users of that flag.
> 
> This came to light when fiddling with the Epson Moverio BT-200 display
> which consists of 2 TC358762 bridges with SPI funneled through
> to the unknown display chip. With that patch the bridge can be accessed,
> Reading back registers works, when the above-mentioned registers are set.
> 
> In Command-Mode update, there was a nop sent, apparently the most
> relevant part was the bta sync to actually force low power mode.
> 
> Video mode panel at OMAP4 (BT-200) and video mode at OMAP5 was tested.
> 
> Fixes: e70965386353e ("drm/omap: dsi: simplify write function")
> Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
Thanks, picking up to drm-misc-next.

  Tomi