linux-kernel - Re: [PATCH] drm: fsl-dcu: enable PIXCLK on LS1021A

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Message-ID: <5015d9c9fe02733f8dfb2714a903ab725e7cdd7f.camel@ew.tq-group.com>
Date:   Thu, 16 Sep 2021 14:50:27 +0200
From:   Matthias Schiffer <matthias.schiffer@...tq-group.com>
To:     Stefan Agner <stefan@...er.ch>, sboyd@...nel.org,
        mturquette@...libre.com
Cc:     Alison Wang <alison.wang@....com>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm: fsl-dcu: enable PIXCLK on LS1021A

On Fri, 2020-08-21 at 15:41 +0200, Stefan Agner wrote:
> Hi Matthias,
> 
> On 2020-08-20 12:58, Matthias Schiffer wrote:
> > The PIXCLK needs to be enabled in SCFG before accessing the DCU on LS1021A,
> > or the access will hang.
> 
> Hm, this seems a rather ad-hoc access to SCFG from the DCU. We do
> support a pixel clock in the device tree bindings of fsl-dcu, so ideally
> we should enable the pixel clock through the clock framework.
> 
> On the other hand, I guess that would mean adding a clock driver to flip
> a single bit, which seems a bit excessive too.
> 
> I'd like a second opinion on that. Adding clk framework maintainers.

It's been a while, and nobody else has given their opinion. How should
we proceed with this patch?

Matthias


> 
> --
> Stefan
> 
> > 
> > Signed-off-by: Matthias Schiffer <matthias.schiffer@...tq-group.com>
> > ---
> >  drivers/gpu/drm/fsl-dcu/Kconfig           |  1 +
> >  drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c | 25 +++++++++++++++++++++++
> >  drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.h |  3 +++
> >  3 files changed, 29 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/fsl-dcu/Kconfig b/drivers/gpu/drm/fsl-dcu/Kconfig
> > index d7dd8ba90e3a..9e5a35e7c00c 100644
> > --- a/drivers/gpu/drm/fsl-dcu/Kconfig
> > +++ b/drivers/gpu/drm/fsl-dcu/Kconfig
> > @@ -8,6 +8,7 @@ config DRM_FSL_DCU
> >  	select DRM_PANEL
> >  	select REGMAP_MMIO
> >  	select VIDEOMODE_HELPERS
> > +	select MFD_SYSCON if SOC_LS1021A
> >  	help
> >  	  Choose this option if you have an Freescale DCU chipset.
> >  	  If M is selected the module will be called fsl-dcu-drm.
> > diff --git a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c
> > b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c
> > index abbc1ddbf27f..8a7556655581 100644
> > --- a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c
> > +++ b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c
> > @@ -51,6 +51,23 @@ static const struct regmap_config fsl_dcu_regmap_config = {
> >  	.volatile_reg = fsl_dcu_drm_is_volatile_reg,
> >  };
> >  
> > +static int fsl_dcu_scfg_config_ls1021a(struct device_node *np)
> > +{
> > +	struct regmap *scfg;
> > +
> > +	scfg = syscon_regmap_lookup_by_compatible("fsl,ls1021a-scfg");
> > +	if (IS_ERR(scfg))
> > +		return PTR_ERR(scfg);
> > +
> > +	/*
> > +	 * For simplicity, enable the PIXCLK unconditionally. It might
> > +	 * be possible to disable the clock in PM or on unload as a future
> > +	 * improvement.
> > +	 */
> > +	return regmap_update_bits(scfg, SCFG_PIXCLKCR, SCFG_PIXCLKCR_PXCEN,
> > +				  SCFG_PIXCLKCR_PXCEN);
> > +}
> > +
> >  static void fsl_dcu_irq_uninstall(struct drm_device *dev)
> >  {
> >  	struct fsl_dcu_drm_device *fsl_dev = dev->dev_private;
> > @@ -70,6 +87,14 @@ static int fsl_dcu_load(struct drm_device *dev,
> > unsigned long flags)
> >  		return ret;
> >  	}
> >  
> > +	if (of_device_is_compatible(fsl_dev->np, "fsl,ls1021a-dcu")) {
> > +		ret = fsl_dcu_scfg_config_ls1021a(fsl_dev->np);
> > +		if (ret < 0) {
> > +			dev_err(dev->dev, "failed to enable pixclk\n");
> > +			goto done;
> > +		}
> > +	}
> > +
> >  	ret = drm_vblank_init(dev, dev->mode_config.num_crtc);
> >  	if (ret < 0) {
> >  		dev_err(dev->dev, "failed to initialize vblank\n");
> > diff --git a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.h
> > b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.h
> > index e2049a0e8a92..566396013c04 100644
> > --- a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.h
> > +++ b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.h
> > @@ -160,6 +160,9 @@
> >  #define FSL_DCU_ARGB4444		12
> >  #define FSL_DCU_YUV422			14
> >  
> > +#define SCFG_PIXCLKCR			0x28
> > +#define SCFG_PIXCLKCR_PXCEN		BIT(31)
> > +
> >  #define VF610_LAYER_REG_NUM		9
> >  #define LS1021A_LAYER_REG_NUM		10