Re: [PATCH v2 3/5] drm/rockchip: vop2: Improve display modes handling on RK3588 HDMI0

[Maxime Ripard <mripard@kernel.org>]

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On Tue, Dec 17, 2024 at 06:36:41PM +0200, Cristian Ciocaltea wrote:
> On 12/17/24 5:00 PM, Maxime Ripard wrote:
> > On Wed, Dec 11, 2024 at 07:01:15PM +0100, Heiko Stübner wrote:
> >> Am Mittwoch, 11. Dezember 2024, 18:47:44 CET schrieb Maxime Ripard:
> >>> On Wed, Dec 11, 2024 at 06:23:03PM +0100, Heiko Stübner wrote:
> >>>> Am Mittwoch, 11. Dezember 2024, 18:07:57 CET schrieb Maxime Ripard:
> >>>>> On Wed, Dec 11, 2024 at 12:15:07PM +0200, Cristian Ciocaltea wrote:
> >>>>>> The RK3588 specific implementation is currently quite limited in terms
> >>>>>> of handling the full range of display modes supported by the connected
> >>>>>> screens, e.g. 2560x1440@75Hz, 2048x1152@60Hz, 1024x768@60Hz are just a
> >>>>>> few of them.
> >>>>>>
> >>>>>> Additionally, it doesn't cope well with non-integer refresh rates like
> >>>>>> 59.94, 29.97, 23.98, etc.
> >>>>>>
> >>>>>> Make use of HDMI0 PHY PLL as a more accurate DCLK source to handle
> >>>>>> all display modes up to 4K@60Hz.
> >>>>>>
> >>>>>> Tested-by: FUKAUMI Naoki <naoki@radxa.com>
> >>>>>> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
> >>>>>> ---
> >>>>>>  drivers/gpu/drm/rockchip/rockchip_drm_vop2.c | 34 ++++++++++++++++++++++++++++
> >>>>>>  1 file changed, 34 insertions(+)
> >>>>>>
> >>>>>> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c
> >>>>>> index 8b2f53ffefdbf1cc8737b3a86e630a03a7fd9348..393fe6aa170aaee9663c4a6d98c1cd6a5ef79392 100644
> >>>>>> --- a/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c
> >>>>>> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c
> >>>>>> @@ -158,6 +158,7 @@ struct vop2_video_port {
> >>>>>>  	struct drm_crtc crtc;
> >>>>>>  	struct vop2 *vop2;
> >>>>>>  	struct clk *dclk;
> >>>>>> +	struct clk *dclk_src;
> >>>>>>  	unsigned int id;
> >>>>>>  	const struct vop2_video_port_data *data;
> >>>>>>  
> >>>>>> @@ -212,6 +213,7 @@ struct vop2 {
> >>>>>>  	struct clk *hclk;
> >>>>>>  	struct clk *aclk;
> >>>>>>  	struct clk *pclk;
> >>>>>> +	struct clk *pll_hdmiphy0;
> >>>>>>  
> >>>>>>  	/* optional internal rgb encoder */
> >>>>>>  	struct rockchip_rgb *rgb;
> >>>>>> @@ -220,6 +222,8 @@ struct vop2 {
> >>>>>>  	struct vop2_win win[];
> >>>>>>  };
> >>>>>>  
> >>>>>> +#define VOP2_MAX_DCLK_RATE		600000 /* kHz */
> >>>>>> +
> >>>>>>  #define vop2_output_if_is_hdmi(x)	((x) == ROCKCHIP_VOP2_EP_HDMI0 || \
> >>>>>>  					 (x) == ROCKCHIP_VOP2_EP_HDMI1)
> >>>>>>  
> >>>>>> @@ -1033,6 +1037,9 @@ static void vop2_crtc_atomic_disable(struct drm_crtc *crtc,
> >>>>>>  
> >>>>>>  	vop2_crtc_disable_irq(vp, VP_INT_DSP_HOLD_VALID);
> >>>>>>  
> >>>>>> +	if (vp->dclk_src)
> >>>>>> +		clk_set_parent(vp->dclk, vp->dclk_src);
> >>>>>> +
> >>>>>>  	clk_disable_unprepare(vp->dclk);
> >>>>>>  
> >>>>>>  	vop2->enable_count--;
> >>>>>> @@ -2049,6 +2056,27 @@ static void vop2_crtc_atomic_enable(struct drm_crtc *crtc,
> >>>>>>  
> >>>>>>  	vop2_vp_write(vp, RK3568_VP_MIPI_CTRL, 0);
> >>>>>>  
> >>>>>> +	/*
> >>>>>> +	 * Switch to HDMI PHY PLL as DCLK source for display modes up
> >>>>>> +	 * to 4K@60Hz, if available, otherwise keep using the system CRU.
> >>>>>> +	 */
> >>>>>> +	if (vop2->pll_hdmiphy0 && mode->crtc_clock <= VOP2_MAX_DCLK_RATE) {
> >>>>>> +		drm_for_each_encoder_mask(encoder, crtc->dev, crtc_state->encoder_mask) {
> >>>>>> +			struct rockchip_encoder *rkencoder = to_rockchip_encoder(encoder);
> >>>>>> +
> >>>>>> +			if (rkencoder->crtc_endpoint_id == ROCKCHIP_VOP2_EP_HDMI0) {
> >>>>>> +				if (!vp->dclk_src)
> >>>>>> +					vp->dclk_src = clk_get_parent(vp->dclk);
> >>>>>> +
> >>>>>> +				ret = clk_set_parent(vp->dclk, vop2->pll_hdmiphy0);
> >>>>>> +				if (ret < 0)
> >>>>>> +					drm_warn(vop2->drm,
> >>>>>> +						 "Could not switch to HDMI0 PHY PLL: %d\n", ret);
> >>>>>> +				break;
> >>>>>> +			}
> >>>>>> +		}
> >>>>>> +	}
> >>>>>> +
> >>>>>
> >>>>> It seems pretty fragile to do it at atomic_enable time, even more so
> >>>>> since you don't lock the parent either.
> >>>>>
> >>>>> Any reason not to do it in the DRM or clock driver probe, and make sure
> >>>>> you never change the parent somehow?
> >>>>
> >>>> On rk3588 we have 3 dclk_s and 2 hdmi controllers. Each video-port can
> >>>> use the clock generated from either the hdmi0phy or hdmi1phy, depending
> >>>> on which hdmi-controller it uses.
> >>>>
> >>>> So you actually need to know which vpX will output to which hdmiY to then
> >>>> reparent that dclk to the hdmiphy output.
> >>>
> >>> The Rockchip nomenclature isn't super obvious to me, sorry. Is there a
> >>> datasheet for this somewhere? Also, does this vpX -> HDMI-Y mapping need
> >>> to be dynamic?
> >>
> >> VPs are CRTCs in drm-language and each of them can drive a differing
> >> number of output encoders. Those video-ports also have differing output
> >> characteristics in terms of supported resolution and other properties.
> >>
> >> The rk3588 TRM has leaked in a number of places, and if you find a
> >> TRM-part2, there is a section labeled "Display Output Interface Description"
> >> that has a nice graphic for that.
> >>
> >> Or in short:
> >> - CRTC(VP)0 supports 8K resolution and can drive DP0+1, HDMI0+1, eDP0+1
> >>   [if I'm reading things correctly, 8K together with CRTC1 somehow)
> >> - CRTC(VP)1 supports 4K resolution and can drive DP0+1, HDMI0+1, eDP0+1
> >> - CRTC(VP)2 supports 4K resolution and can drive DP0+1, HDMI0+1, eDP01, DSI0+1
> >> - CRTC(VP)3 supports 2K resolution and can drive DSI0+1 and some BT1120,BT656
> >>
> >> so for the 3 higher resolution CRTCs there are essentially 6 or 8 output options
> >> depending on the board design
> > 
> > That's much clearer, thanks. I'm not entirely sure how that links to the
> > need for the PLL to change its parent depending on the ouput. Do you
> > need to always have all the outputs on the same PLL?
> 
> One of the problems is that the PHY PLLs cannot be used as clock sources
> for resolutions above 4K@60Hz, while VOP2 on RK3588 supports up to 8K@60Hz,
> which is supposed to be handled by the system CRU.

But can that system CRU drive resolutions lower than 4k@60? If so, why
do we bother with PHYs?

> Moreover, the 2 PLLs are shared between 3 out of the 4 video ports already
> mentioned by Heiko.  There is quite a bit of complexity in downstream
> driver to handle all possible usecases - see [1] for a brief description on
> how was that designed to work.

That's a generic allocation issue. Multiple drivers (vc4 for example)
has this issue for other components. It can be fairly easily dealt with
at atomic_check time.

Maxime

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