Re: [PATCH 7/7] drm/vc4: hdmi: Defer pixel clock validation to HDMI helpers

[Cristian Ciocaltea <cristian.ciocaltea@collabora.com>]

Hi Dave,

On 10/8/26 9:01 PM, Dave Stevenson wrote:
> Hi Cristian
> 
> Sorry for coming in late on this one.
> 
> On Thu, 1 Oct 2026 at 01:27, Cristian Ciocaltea
> <cristian.ciocaltea@collabora.com> wrote:
>>
>> drm_atomic_helper_connector_hdmi_check() rejects modes whose computed
>> TMDS character rate exceeds the connector limit before invoking the
>> driver's .tmds_char_rate_valid() hook.
>>
>> BCM2835 is capped at 162 MHz, slightly below the 165 MHz limit of HDMI
>> 1.2.
> 
> Nothing I have says that BCM2835 is HDMI capped at 162MHz.
> Working back through the history, originally the HSM clock was always
> set to 163.7MHz and the pixel rate had to be >1% below that, hence
> below 162MHz.
> 
> However that was reworked so that the HSM clock rate is now set to the
> pixel clock * 101/100.
> The HSM clock can run at 166.65MHz without issue, so a pixel clock of
> 165MHz is fine.

Thanks for checking this out. 

Since that would be a functional change, I think it's worth introducing a
dedicated patch, acting as a prerequisite to the current one. I'll handle it 
in v2.

Speaking of which, assuming no additional changes are required, would you be
able to merge the series afterwards? That would get us one step closer to
finalizing the infrastructure cleanup.

Cristian