[PATCH v3 0/5] video: Improve syncing performance with cyclic

[Caleb Connolly]

Hi Simon,

On 04/07/2024 09:48, Simon Glass wrote:
> Now that U-Boot has a background-processing feature, it is possible to
> reduce the amount of 'foreground' syncing of the display. At present
> this happens quite often.
> 
> Foreground syncing blocks all other processing, sometimes for 10ms or
> more. When pasting commands into U-Boot over the UART, this typically
> result in characters being dropped. For example, on rpi_4 it isn't
> possible to paste in more than 35 characters before things fail. This
> makes updating the environment or entering long commands very painful
> over the console, since text must be pasted in chunks, or the
> vidconsole device must be dropped from stdout.

I'm not intimately familiar with U-Boots event loop, but to me this 
sounds more like a bug in the console code. I can confirm this issue 
appears on Qualcomm platforms with the GENI serial driver, I tried 
enabling CONFIG_SERIAL_RX_BUFFER and it seemed to help significantly 
(though there were still a few dropped characters when pasting).

Of note, the USB ACM serial driver doesn't seem to have any issues here, 
presumably since it isn't restricted by the baud rate.

If there is an abort, does this approach still ensure that it gets 
printed properly on the video console?

Kind regards,
> 
> This series introduces background syncing, enabled by default for
> boards which use video. The sync rates for foreground and background
> are configurable.
> 
> With this series it is possible to paste in any amount of text to the
> command line. Some sandbox-specific workarounds can now be removed and
> sandbox video (./u-boot -Dl) is significantly more responsive.
> 
> This obviously increases code size, since it enables a subsystem not
> normally used by default. However it only applies to boards which have
> VIDEO enabled, which are presumably less worried about memory space
> since the video code is fairly large.
> 
> Also it is possible to disable CMD_CYCLIC and reduce the growth to:
> 
>     aarch64: (for 1/1 boards) all +1081.0 rodata +65.0 text +1016.0
>         arm: (for 1/1 boards) all +945.0 rodata +65.0 text +880.0
> 
> Without that, the increase doubles.
> 
> It is of course possible to disable CYCLIC and still use VIDEO but this
> reverts to the current behaviour
> 
> Changes in v3:
> - Drop inclusion of kconfig.h in cyclic.h
> - Adapt to new cyclic API
> 
> Changes in v2:
> - Add an SPL_CYCLIC symbol
> - Add a lot more explanation about the header files
> - Expand help for CONFIG_VIDEO
> - Fix 'groth' and 'work-around' typos in cover letter
> 
> Simon Glass (5):
>    cyclic: Add a symbol for SPL
>    video: Move last_sync to private data
>    video: Use cyclic to handle video sync
>    sandbox: Increase cyclic CPU-time limit
>    sandbox: Drop video-sync in serial driver
> 
>   common/Kconfig                    |  9 ++++++
>   common/Makefile                   |  2 +-
>   drivers/serial/sandbox.c          |  2 --
>   drivers/video/Kconfig             | 35 +++++++++++++++++++++
>   drivers/video/video-uclass.c      | 52 +++++++++++++++++++++++++------
>   drivers/watchdog/Kconfig          |  1 +
>   include/asm-generic/global_data.h |  2 +-
>   include/cyclic.h                  |  5 +--
>   include/video.h                   |  2 ++
>   9 files changed, 95 insertions(+), 15 deletions(-)
> 

-- 
// Caleb (they/them)