Re: [PATCH v2 07/12] drm/rockchip: dw_dp: Implement out-of-band HPD handling

[Sebastian Reichel <sebastian.reichel@collabora.com>]

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Hello Chaoyi,

On Tue, Jun 02, 2026 at 04:30:59PM +0800, Chaoyi Chen wrote:
> On 5/1/2026 6:20 AM, Sebastian Reichel wrote:
> > Implement out-of-band hotplug handling, which will be used to receive
> > external hotplug information from the USB-C state machine. This is
> > currently handled by the USBDP PHY, which brings quite some trouble
> > as the register being accessed requires the power-domain from the DP
> > controller and also requires custom TypeC HPD info parsing in the
> > USBDP PHY driver.
> > 
> > In contrast to the USBDP PHY this does not just enable the hotplug
> > signal when a DP AltMode capable adapter is plugged in, but instead
> > properly detects if a cable is plugged in for things like USB-C to
> > HDMI adapters.
> > 
> > Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
> 
> [...]
> 
> > +static void dw_dp_rockchip_hpd_sw_cfg(void *data, bool hpd)
> > +{
> > +	struct rockchip_dw_dp *dp = data;
> > +	u32 hpd_reg = dp->pdata->hpd_reg[dp->id];
> > +
> > +	dev_dbg(dp->dev, "Force HPD connected=%s\n", str_yes_no(hpd));
> > +
> > +	dp->hpd_cfg = hpd;
> > +
> > +	regmap_write(dp->vo_grf, hpd_reg,
> > +		     FIELD_PREP_WM16_CONST(ROCKCHIP_VO_GRF_DP_SINK_HPD_CFG, dp->hpd_cfg));
> 
> FIELD_PREP_WM16() should be used here because "dp->hpd_cfg" is not
> a constant expression.
> 
> Other patches in this series have similar issues. Doesn't your
> compiler warn you about this? Thanks.

The code builds warning free for me. Also FIELD_PREP_WM16_CONST
requies that the mask is constant, which is the first argument
(i.e. ROCKCHIP_VO_GRF_DP_SINK_HPD_CFG in this case). The second
argument should be fine as a variable as far as I can tell.

But since FIELD_PREP_WM16 is shorter anyways, gives better error
handling and can be used for all occuances in the dw-dp rockchip
glue I will use that instead.

Thanks,

-- Sebastian

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