Message-ID: <20190607113540.GB7593@pendragon.ideasonboard.com>
Date:   Fri, 7 Jun 2019 14:35:40 +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,

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 ?

> +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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