Date:   Fri, 7 Jun 2019 14:44:57 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Jacopo Mondi <jacopo+renesas@...ndi.org>
Cc:     kieran.bingham+renesas@...asonboard.com, airlied@...ux.ie,
        daniel@...ll.ch, koji.matsuoka.xm@...esas.com, muroya@....co.jp,
        VenkataRajesh.Kalakodima@...bosch.com,
        Harsha.ManjulaMallikarjun@...bosch.com,
        linux-renesas-soc@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 14/20] drm: rcar-du: Add support for CMM

Hi Jacopo,

On Fri, Jun 07, 2019 at 02:35:40PM +0300, Laurent Pinchart wrote:
> Hi Jacopo,
> 
> Thank you for the patch.
> 
> On Thu, Jun 06, 2019 at 04:22:14PM +0200, Jacopo Mondi wrote:
> > Add a driver for the R-Car Display Unit Color Correction Module.
> > 
> > Each DU output channel is provided with a CMM unit to perform image
> > enhancement and color correction.
> 
> I would say "On most Gen3 SoCs, each DU ..." as V3* SoCs have no CMM.
> 
> > 
> > Add support for CMM through a driver that supports configuration of
> > the 1-dimensional LUT table. More advanced CMM feature could be
> > implemented on top of this basic one.
> 
> s/could be/will be/ ? :-)
> 
> > 
> > Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
> > ---
> >  drivers/gpu/drm/rcar-du/Kconfig    |   7 +
> >  drivers/gpu/drm/rcar-du/Makefile   |   1 +
> >  drivers/gpu/drm/rcar-du/rcar_cmm.c | 197 +++++++++++++++++++++++++++++
> >  drivers/gpu/drm/rcar-du/rcar_cmm.h |  38 ++++++
> >  4 files changed, 243 insertions(+)
> >  create mode 100644 drivers/gpu/drm/rcar-du/rcar_cmm.c
> >  create mode 100644 drivers/gpu/drm/rcar-du/rcar_cmm.h
> > 
> > diff --git a/drivers/gpu/drm/rcar-du/Kconfig b/drivers/gpu/drm/rcar-du/Kconfig
> > index 1529849e217e..539d232790d1 100644
> > --- a/drivers/gpu/drm/rcar-du/Kconfig
> > +++ b/drivers/gpu/drm/rcar-du/Kconfig
> > @@ -13,6 +13,13 @@ config DRM_RCAR_DU
> >  	  Choose this option if you have an R-Car chipset.
> >  	  If M is selected the module will be called rcar-du-drm.
> >  
> > +config DRM_RCAR_CMM
> > +	bool "R-Car DU Color Management Module (CMM) Support"
> > +	depends on DRM && OF
> > +	depends on DRM_RCAR_DU
> > +	help
> > +	  Enable support for R-Car Color Management Module (CMM).
> > +
> >  config DRM_RCAR_DW_HDMI
> >  	tristate "R-Car DU Gen3 HDMI Encoder Support"
> >  	depends on DRM && OF
> > diff --git a/drivers/gpu/drm/rcar-du/Makefile b/drivers/gpu/drm/rcar-du/Makefile
> > index 6c2ed9c46467..4d1187ccc3e5 100644
> > --- a/drivers/gpu/drm/rcar-du/Makefile
> > +++ b/drivers/gpu/drm/rcar-du/Makefile
> > @@ -15,6 +15,7 @@ rcar-du-drm-$(CONFIG_DRM_RCAR_LVDS)	+= rcar_du_of.o \
> >  rcar-du-drm-$(CONFIG_DRM_RCAR_VSP)	+= rcar_du_vsp.o
> >  rcar-du-drm-$(CONFIG_DRM_RCAR_WRITEBACK) += rcar_du_writeback.o
> >  
> > +obj-$(CONFIG_DRM_RCAR_CMM)		+= rcar_cmm.o
> >  obj-$(CONFIG_DRM_RCAR_DU)		+= rcar-du-drm.o
> >  obj-$(CONFIG_DRM_RCAR_DW_HDMI)		+= rcar_dw_hdmi.o
> >  obj-$(CONFIG_DRM_RCAR_LVDS)		+= rcar_lvds.o
> > diff --git a/drivers/gpu/drm/rcar-du/rcar_cmm.c b/drivers/gpu/drm/rcar-du/rcar_cmm.c
> > new file mode 100644
> > index 000000000000..5d9d917b91f4
> > --- /dev/null
> > +++ b/drivers/gpu/drm/rcar-du/rcar_cmm.c
> > @@ -0,0 +1,197 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * rcar_cmm.c -- R-Car Display Unit Color Management Module
> > + *
> > + * Copyright (C) 2019 Jacopo Mondi <jacopo+renesas@...ndi.org>
> > + */
> > +
> > +#include <linux/clk.h>
> > +#include <linux/io.h>
> > +#include <linux/module.h>
> > +#include <linux/of.h>
> > +#include <linux/platform_device.h>
> > +
> > +#include <drm/drm_atomic.h>
> > +
> > +#include "rcar_cmm.h"
> > +
> > +#define CM2_LUT_CTRL		0x00
> 
> I would write all register addresses with 3 (or 4) digits.
> 
> > +#define CM2_LUT_CTRL_EN		BIT(0)
> > +#define CM2_LUT_TBLA		0x600
> 
> I would define this as
> 
> #define CM2_LUT_TBLA(n)		(0x600 + (n) * 4)
> 
> > +
> > +struct rcar_cmm {
> > +	struct clk *clk;
> > +	void __iomem *base;
> > +	bool enabled;
> > +
> > +	/* LUT table scratch buffer. */
> > +	struct {
> > +		bool restore;
> > +		unsigned int size;
> > +		uint32_t table[CMM_GAMMA_LUT_SIZE];
> > +	} lut;
> > +};
> > +
> > +static inline int rcar_cmm_read(struct rcar_cmm *rcmm, u32 reg)
> > +{
> > +	return ioread32(rcmm->base + reg);
> > +}
> > +
> > +static inline void rcar_cmm_write(struct rcar_cmm *rcmm, u32 reg, u32 data)
> > +{
> > +	iowrite32(data, rcmm->base + reg);
> > +}
> > +
> > +int rcar_cmm_setup(struct platform_device *pdev, struct rcar_cmm_config *config)
> 
> Please document the functions exposed to the DU driver. It's hard to
> understand the setup vs. enable/disable split by just reading this
> driver.
> 
> > +{
> > +	struct rcar_cmm *rcmm = platform_get_drvdata(pdev);
> > +	unsigned int i;
> > +
> > +	if (config->lut.size > CMM_GAMMA_LUT_SIZE)
> > +		return -EINVAL;
> > +
> > +	/*
> > +	 * As cmm_setup is called by atomic commit tail helper, it might be
> > +	 * called before the enabling the CRTC (which calls cmm_enable()).
> > +	 *
> > +	 * Store the LUT table entries in the scratch buffer to be later
> > +	 * programmed at enable time.
> > +	 */
> > +	if (!rcmm->enabled) {
> > +		if (!config->lut.enable)
> > +			return 0;
> > +
> > +		for (i = 0; i < config->lut.size; ++i) {
> > +			struct drm_color_lut *lut = &config->lut.table[i];
> > +
> > +			rcmm->lut.table[i] = (lut->red & 0xff) << 16 |
> > +					     (lut->green & 0xff) << 8 |
> > +					     (lut->blue & 0xff);
> > +		}
> > +
> > +		rcmm->lut.restore = true;
> > +		rcmm->lut.size = config->lut.size;
> > +
> > +		return 0;
> > +	}
> > +
> > +	if (rcar_cmm_read(rcmm, CM2_LUT_CTRL) & CM2_LUT_CTRL_EN &&
> > +	    !config->lut.enable) {
> > +		rcar_cmm_write(rcmm, CM2_LUT_CTRL, 0);
> > +		return 0;
> > +	}
> > +
> > +	/* Enable LUT and program the new gamma table values. */
> > +	rcar_cmm_write(rcmm, CM2_LUT_CTRL, CM2_LUT_CTRL_EN);
> 
> Shouldn't you write the LUT contents before enabling it (same below) ?
> 
> > +	for (i = 0; i < config->lut.size; ++i) {
> > +		struct drm_color_lut *lut = &config->lut.table[i];
> > +		u32 val = (lut->red & 0xff) << 16 | (lut->green & 0xff) << 8 |
> > +			  (lut->blue & 0xff);
> 
> Do you need to recompute the value, can't you use rcmm->lut.table ?
> 
> > +
> > +		rcar_cmm_write(rcmm, CM2_LUT_TBLA + i * 4, val);
> > +	}
> > +
> > +	return 0;
> > +}
> 
> You need to export this and the next two functions.
> 
> > +
> > +int rcar_cmm_enable(struct platform_device *pdev)
> > +{
> > +	struct rcar_cmm *rcmm = platform_get_drvdata(pdev);
> > +	unsigned int i;
> > +	int ret;
> > +
> > +	if (rcmm->enabled)
> > +		return 0;
> 
> Can this happen without a bug in the caller ? If it can, and assuming
> the caller balances the enable and disable calls, you will have
> unbalanced clk_prepare_enable() and clk_disable_unprepare() calls.
> 
> > +
> > +	ret = clk_prepare_enable(rcmm->clk);
> > +	if (ret)
> > +		return ret;
> 
> Could you use pm_runtime_get_sync() instead ?
> 
> > +
> > +	/* Apply the LUT table values saved at cmm_setup time. */
> > +	if (rcmm->lut.restore) {
> > +		rcar_cmm_write(rcmm, CM2_LUT_CTRL, CM2_LUT_CTRL_EN);
> > +		for (i = 0; i < rcmm->lut.size; ++i)
> > +			rcar_cmm_write(rcmm, CM2_LUT_TBLA + i * 4,
> > +				       rcmm->lut.table[i]);
> > +
> > +		rcmm->lut.restore = false;
> > +		rcmm->lut.size = 0;
> > +	}
> > +
> > +	rcmm->enabled = true;
> > +
> > +	return 0;
> > +}
> > +
> > +void rcar_cmm_disable(struct platform_device *pdev)
> > +{
> > +	struct rcar_cmm *rcmm = platform_get_drvdata(pdev);
> > +
> > +	rcar_cmm_write(rcmm, CM2_LUT_CTRL, 0);
> > +
> > +	clk_disable_unprepare(rcmm->clk);
> > +
> > +	rcmm->lut.restore = false;
> > +	rcmm->lut.size = 0;
> > +	rcmm->enabled = false;
> > +}
> > +
> > +static int rcar_cmm_probe(struct platform_device *pdev)
> > +{
> > +	struct rcar_cmm *rcmm;
> > +	struct resource *res;
> > +	resource_size_t size;
> > +
> > +	rcmm = devm_kzalloc(&pdev->dev, sizeof(*rcmm), GFP_KERNEL);
> > +	if (!rcmm)
> > +		return -ENOMEM;
> > +
> > +	platform_set_drvdata(pdev, rcmm);
> > +
> > +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> > +	size = resource_size(res);
> > +	if (!devm_request_mem_region(&pdev->dev, res->start, size,
> > +				     dev_name(&pdev->dev))) {
> > +		dev_err(&pdev->dev,
> > +			"can't request region for resource %pR\n", res);
> > +		return -EBUSY;
> > +	}
> > +
> > +	rcmm->base = devm_ioremap_nocache(&pdev->dev, res->start, size);
> > +	if (IS_ERR(rcmm->base))
> > +		return PTR_ERR(rcmm->base);
> 
> Anything wrong with devm_ioremap_resource() ?
> 
> > +
> > +	rcmm->clk = devm_clk_get(&pdev->dev, NULL);
> > +	if (IS_ERR(rcmm->clk)) {
> > +		dev_err(&pdev->dev, "Failed to get CMM clock");
> > +		return PTR_ERR(rcmm->clk);
> > +	}
> > +
> > +	rcmm->lut.restore = false;
> > +	rcmm->lut.size = 0;
> > +	rcmm->enabled = false;
> 
> As you allocate memory with kzalloc() you could skip this.
> 
> > +
> > +	return 0;
> > +}
> > +
> > +static const struct of_device_id rcar_cmm_of_table[] = {
> > +	{ .compatible = "renesas,cmm-gen3" },
> > +	{ .compatible = "renesas,cmm-gen2" },
> > +	{ },
> > +};
> > +
> > +MODULE_DEVICE_TABLE(of, rcar_cmm_of_table);
> > +
> > +static struct platform_driver rcar_cmm_platform_driver = {
> > +	.probe		= rcar_cmm_probe,
> > +	.driver		= {
> > +		.name	= "rcar-cmm",
> > +		.of_match_table = rcar_cmm_of_table,
> > +	},
> 
> No need for suspend/resume support ? The DU driver should disable/enable
> the CMM in its suspend/resume paths, so this should be fine, but won't
> the LUT contents be lost and need to be restored ?
> 
> > +};
> > +
> > +module_platform_driver(rcar_cmm_platform_driver);
> > +
> > +MODULE_AUTHOR("Jacopo Mondi <jacopo+renesas@...ndi.org");
> 
> Missing >.
> 
> > +MODULE_DESCRIPTION("Renesas R-Car CMM Driver");
> > +MODULE_LICENSE("GPL v2");
> > diff --git a/drivers/gpu/drm/rcar-du/rcar_cmm.h b/drivers/gpu/drm/rcar-du/rcar_cmm.h
> > new file mode 100644
> > index 000000000000..da61a145dc5c
> > --- /dev/null
> > +++ b/drivers/gpu/drm/rcar-du/rcar_cmm.h
> > @@ -0,0 +1,38 @@
> > +/* SPDX-License-Identifier: GPL-2.0+ */
> 
> The .c and .h file licenses don't match.
> 
> > +/*
> > + * rcar_cmm.h -- R-Car Display Unit Color Management Module
> > + *
> > + * Copyright (C) 2019 Jacopo Mondi <jacopo+renesas@...ndi.org>
> > + */
> > +
> > +#ifndef __RCAR_CMM_H__
> > +#define __RCAR_CMM_H__
> > +
> > +#include <linux/platform_device.h>
> 
> You can forward-declare struct platform_device instead.
> 
> > +
> > +#define CMM_GAMMA_LUT_SIZE		256
> > +
> > +struct drm_color_lut;
> > +
> > +/**
> > + * struct rcar_cmm_config - CMM configuration
> > + *
> > + * @lut:	1D-LUT configuration
> > + * @lut.enable:	1D-LUT enable flag
> > + * @lut.table:	1D-LUT table entries.
> > + * @lut.size	1D-LUT number of entries. Max is 256
> 
> The last line is missing a colon.
> 
> > + */
> > +struct rcar_cmm_config {
> > +	struct {
> > +		bool enable;
> > +		struct drm_color_lut *table;
> > +		unsigned int size;
> > +	} lut;
> > +};
> > +
> > +int rcar_cmm_enable(struct platform_device *);
> 
> As the OF API looks up a struct device from a device_node, should we use
> struct device here ?

My bad, the API actually returns a struct platform_device. I would still
prefer using struct device, but it then becomes more of a personal
preference.

> > +void rcar_cmm_disable(struct platform_device *);
> 
> I find headers more readable when function arguments are named. In this
> case the types probably provide enough information, but good luck trying
> to read a function such as
> 
> int foo(int, int, bool);
> 
> > +
> > +int rcar_cmm_setup(struct platform_device *, struct rcar_cmm_config *);
> 
> Can the second argument be const ?
> 
> > +
> > +#endif /* __RCAR_CMM_H__ */

-- 
Regards,

Laurent Pinchart

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