Re: [PATCH v1 2/4] xlnx_dp: Introduce a vblank signal

[Peter Maydell]

On Tue, 3 May 2022 at 16:27, <frederic.konrad@xilinx.com> wrote:
>
> From: Sai Pavan Boddu <sai.pavan.boddu@xilinx.com>
>
> Add a periodic timer which raises vblank at a frequency of 30Hz.
>
> Signed-off-by: Sai Pavan Boddu <saipava@xilinx.com>
> Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
> Changes by fkonrad:
>   - Switched to transaction-based ptimer API.
>   - Added the DP_INT_VBLNK_START macro.
> Signed-off-by: Frederic Konrad <fkonrad@amd.com>
> ---


> @@ -1309,6 +1323,10 @@ static void xlnx_dp_realize(DeviceState *dev, Error 
> **errp)
>                                             &as);
>      AUD_set_volume_out(s->amixer_output_stream, 0, 255, 255);
>      xlnx_dp_audio_activate(s);
> +    s->vblank = ptimer_init(vblank_hit, s, PTIMER_POLICY_DEFAULT);
> +    ptimer_transaction_begin(s->vblank);
> +    ptimer_set_freq(s->vblank, 30);
> +    ptimer_transaction_commit(s->vblank);

The ptimer documentation (in include/hw/ptimer.h) says
 * The default ptimer policy retains backward compatibility with the legacy
 * timers. Custom policies are adjusting the default one. Consider providing
 * a correct policy for your timer.

and goes on to describe various weird behaviours of the default
policy. You almost certainly don't want to use PTIMER_POLICY_DEFAULT
for a new timer -- instead figure out the behaviour you actually
want and specify the appropriate flags.

thanks
-- PMM