Re: [PATCH v12 01/16] drm/bridge: dw-hdmi-qp: Demote i2c bus error messages to debug level

[Diederik de Haas]

Hi Cristian,

On Mon Oct 5, 2026 at 2:38 AM CEST, Cristian Ciocaltea wrote:
> A NACK or timeout on the DDC bus is a normal condition when the sink is
> absent or unpowered.  Some displays keep HPD asserted and the EDID
> EEPROM readable while in standby, but leave the SCDC slave unpowered.
> This results in i2c-related error messages on every boot during
> scrambling setup, even though the condition is handled gracefully and
> the SCDC configuration is restored on the next hotplug event.
>
> Log the i2c bus level failures with dev_dbg_ratelimited() instead,
> matching the silent behaviour of the non-QP dw-hdmi i2c bus algorithm.

I can confirm that with this patch I no longer see warnings like this:

  dwhdmiqp-rockchip fde80000.hdmi: i2c read error
  dwhdmiqp-rockchip fde80000.hdmi: i2c write nack!

When I add ``dw_hdmi_qp.dyndbg`` to the kernel command line, I do see
them at debug level.
This is when I boot up my NanoPC-T6 LTS connected to my 4K TV while it
is turned OFF.

When I boot up my NanoPC-T6 LTS connected to my 4K TV while it is
turned ON, dmesg is rather clean wrt dw_hdmi_qp both with and without
``dw_hdmi_qp.dyndbg`` in my kernel command line.

So it acts exactly as intended :-) Thus feel free to include my:

Tested-by: Diederik de Haas <diederik@xxxxxxxxxxxxxx>  # NanoPC-T6 LTS

Thanks!

Cheers,
  Diederik

> The DDC users already report failures at the appropriate level, e.g. the
> SCDC helpers via drm_scdc_dbg().  This also makes the no-hpd special
> casing of the read path messages redundant, so drop it.
>
> Reported-by: Diederik de Haas <diederik@xxxxxxxxxxxxxx>
> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@xxxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c | 16 ++++------------
>  1 file changed, 4 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
> index c9568aea98dc..9abcea92b720 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
> @@ -350,22 +350,14 @@ static int dw_hdmi_qp_i2c_read(struct dw_hdmi_qp *hdmi,
>  
>  		stat = wait_for_completion_timeout(&i2c->cmp, HZ / 10);
>  		if (!stat) {
> -			if (hdmi->no_hpd)
> -				dev_dbg_ratelimited(hdmi->dev,
> -						    "i2c read timed out\n");
> -			else
> -				dev_err(hdmi->dev, "i2c read timed out\n");
> +			dev_dbg_ratelimited(hdmi->dev, "i2c read timed out\n");
>  			dw_hdmi_qp_write(hdmi, 0x01, I2CM_CONTROL0);
>  			return -EAGAIN;
>  		}
>  
>  		/* Check for error condition on the bus */
>  		if (i2c->stat & I2CM_NACK_RCVD_IRQ) {
> -			if (hdmi->no_hpd)
> -				dev_dbg_ratelimited(hdmi->dev,
> -						    "i2c read error\n");
> -			else
> -				dev_err(hdmi->dev, "i2c read error\n");
> +			dev_dbg_ratelimited(hdmi->dev, "i2c read error\n");
>  			dw_hdmi_qp_write(hdmi, 0x01, I2CM_CONTROL0);
>  			return -EIO;
>  		}
> @@ -404,14 +396,14 @@ static int dw_hdmi_qp_i2c_write(struct dw_hdmi_qp *hdmi,
>  
>  		stat = wait_for_completion_timeout(&i2c->cmp, HZ / 10);
>  		if (!stat) {
> -			dev_err(hdmi->dev, "i2c write time out!\n");
> +			dev_dbg_ratelimited(hdmi->dev, "i2c write time out!\n");
>  			dw_hdmi_qp_write(hdmi, 0x01, I2CM_CONTROL0);
>  			return -EAGAIN;
>  		}
>  
>  		/* Check for error condition on the bus */
>  		if (i2c->stat & I2CM_NACK_RCVD_IRQ) {
> -			dev_err(hdmi->dev, "i2c write nack!\n");
> +			dev_dbg_ratelimited(hdmi->dev, "i2c write nack!\n");
>  			dw_hdmi_qp_write(hdmi, 0x01, I2CM_CONTROL0);
>  			return -EIO;
>  		}