Re: [PATCH v3 1/4] drm/dp: Add helper to set LTTPRs in transparent mode

[Abel Vesa <abel.vesa@linaro.org>]

On 25-01-07 10:30:29, Johan Hovold wrote:
> On Fri, Jan 03, 2025 at 02:58:15PM +0200, Abel Vesa wrote:
> > According to the DisplayPort standard, LTTPRs have two operating
> > modes:
> >  - non-transparent - it replies to DPCD LTTPR field specific AUX
> >    requests, while passes through all other AUX requests
> >  - transparent - it passes through all AUX requests.
> > 
> > Switching between this two modes is done by the DPTX by issuing
> > an AUX write to the DPCD PHY_REPEATER_MODE register.
> > 
> > Add a generic helper that allows switching between these modes.
> > 
> > Also add a generic wrapper for the helper that handles the explicit
> > disabling of non-transparent mode and its disable->enable sequence
> > mentioned in the DP Standard v2.0 section 3.6.6.1. Do this in order
> > to move this handling out of the vendor specific driver implementation
> > into the generic framework.
> > 
> > Tested-by: Johan Hovold <johan+linaro@kernel.org>
> > Signed-off-by: Abel Vesa <abel.vesa@linaro.org>
> 
> > +/**
> > + * drm_dp_lttpr_init - init LTTPR transparency mode according to DP standard
> > + *
> > + * @aux: DisplayPort AUX channel
> > + * @lttpr_count: Number of LTTPRs. Between 0 and 8, according to DP standard.
> > + *               Negative error code for any non-valid number.
> > + *               See drm_dp_lttpr_count().
> > + *
> > + * Returns 0 on success or a negative error code on failure.
> > + */
> > +int drm_dp_lttpr_init(struct drm_dp_aux *aux, int lttpr_count)
> > +{
> > +	int ret;
> > +
> > +	if (!lttpr_count)
> > +		return 0;
> > +
> > +	/*
> > +	 * See DP Standard v2.0 3.6.6.1 about the explicit disabling of
> > +	 * non-transparent mode and the disable->enable non-transparent mode
> > +	 * sequence.
> > +	 */
> > +	ret = drm_dp_lttpr_set_transparent_mode(aux, true);
> > +	if (ret)
> > +		return ret;
> > +
> > +	if (lttpr_count < 0)
> > +		return -ENODEV;
> > +
> > +	/*
> > +	 * Roll-back to tranparent mode if setting non-tranparent mode failed
> 
> typo: transparent (2x)

Will fix.

> 
> > +	 */
> 
> I think this comment now needs to go inside the conditional, if you want
> to keep it at all.

Yes, will move it.

> 
> > +	if (drm_dp_lttpr_set_transparent_mode(aux, false)) {
> > +		drm_dp_lttpr_set_transparent_mode(aux, true);
> > +		return -EINVAL;
> > +	}
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL(drm_dp_lttpr_init);
> 
> This looks much better to me now, so with the above addressed: 
> 
> Reviewed-by: Johan Hovold <johan+linaro@kernel.org>

Thanks for reviewing!

Abel