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Date:   Thu, 8 Sep 2022 12:26:37 -0300
From:   Wander Lairson Costa <wander@redhat.com>
To:     Charles Mirabile <cmirabil@redhat.com>
Cc:     linux-kernel@vger.kernel.org,
        Peter Robinson <pbrobinson@gmail.com>,
        Serge Schneider <serge@raspberrypi.org>,
        Stefan Wahren <stefan.wahren@i2se.com>,
        Nicolas Saenz Julienne <nicolassaenzj@gmail.com>,
        Mattias Brugger <mbrugger@suse.com>,
        linux-rpi-kernel@lists.infradead.org,
        linux-arm-kernel@lists.infradead.org, rh-kdlp@googlegroups.com,
        Miguel Ojeda <ojeda@kernel.org>,
        Joel Savitz <jsavitz@redhat.com>
Subject: Re: [PATCH 2/5] drivers/auxdisplay: sensehat: Raspberry Pi Sense HAT
 display driver
Message-ID: <YxoJrZDJbh+GYAn8@fedora>
References: <20220823174158.45579-1-cmirabil@redhat.com>
 <20220823174158.45579-3-cmirabil@redhat.com>
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On Tue, Aug 23, 2022 at 01:41:55PM -0400, Charles Mirabile wrote:
> This patch adds the driver for the 8x8 RGB LED matrix display
> on the Sense HAT. It appears as a character device named sense-hat
> in /dev/. That special file is 192 bytes large and contains 64
> RGB triplets (3 bytes each) one for each pixel in row major order.
> 
> Co-developed-by: Joel Savitz <jsavitz@redhat.com>
> Signed-off-by: Joel Savitz <jsavitz@redhat.com>
> Signed-off-by: Charles Mirabile <cmirabil@redhat.com>
> ---
>  drivers/auxdisplay/Kconfig            |   8 +
>  drivers/auxdisplay/Makefile           |   1 +
>  drivers/auxdisplay/sensehat-display.c | 205 ++++++++++++++++++++++++++
>  3 files changed, 214 insertions(+)
>  create mode 100644 drivers/auxdisplay/sensehat-display.c
> 
> diff --git a/drivers/auxdisplay/Kconfig b/drivers/auxdisplay/Kconfig
> index 64012cda4d12..9bad1aade7a0 100644
> --- a/drivers/auxdisplay/Kconfig
> +++ b/drivers/auxdisplay/Kconfig
> @@ -203,6 +203,14 @@ config ARM_CHARLCD
>  	  line and the Linux version on the second line, but that's
>  	  still useful.
>  
> +config SENSEHAT_DISPLAY
> +	tristate "Raspberry Pi Sense HAT display driver"
> +	depends on I2C
> +	select MFD_SIMPLE_MFD_I2C
> +	help
> +	 This is a driver for the Raspberry Pi Sensehat 8x8 RBG-LED matrix
> +	 you can access it as a misc device at /dev/sense-hat
> +
>  menuconfig PARPORT_PANEL
>  	tristate "Parallel port LCD/Keypad Panel support"
>  	depends on PARPORT
> diff --git a/drivers/auxdisplay/Makefile b/drivers/auxdisplay/Makefile
> index 6968ed4d3f0a..30b2b7934046 100644
> --- a/drivers/auxdisplay/Makefile
> +++ b/drivers/auxdisplay/Makefile
> @@ -14,3 +14,4 @@ obj-$(CONFIG_HT16K33)		+= ht16k33.o
>  obj-$(CONFIG_PARPORT_PANEL)	+= panel.o
>  obj-$(CONFIG_LCD2S)		+= lcd2s.o
>  obj-$(CONFIG_LINEDISP)		+= line-display.o
> +obj-$(CONFIG_SENSEHAT_DISPLAY)	+= sensehat-display.o
> diff --git a/drivers/auxdisplay/sensehat-display.c b/drivers/auxdisplay/sensehat-display.c
> new file mode 100644
> index 000000000000..08c0c4338f3e
> --- /dev/null
> +++ b/drivers/auxdisplay/sensehat-display.c
> @@ -0,0 +1,205 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Raspberry Pi Sense HAT 8x8 LED matrix display driver
> + * http://raspberrypi.org
> + *
> + * Copyright (C) 2015 Raspberry Pi
> + * Copyright (C) 2021 Charles Mirabile, Joel Savitz
> + *
> + * Original Author: Serge Schneider
> + * Revised for upstream Linux by: Charles Mirabile, Joel Savitz
> + */
> +
> +#include <linux/module.h>
> +#include <linux/kernel.h>
> +#include <linux/errno.h>
> +#include <linux/string.h>
> +#include <linux/mm.h>
> +#include <linux/slab.h>
> +#include <linux/uaccess.h>
> +#include <linux/delay.h>
> +#include <linux/init.h>
> +#include <linux/platform_device.h>
> +#include <linux/mod_devicetable.h>
> +#include <linux/miscdevice.h>
> +#include <linux/regmap.h>
> +#include <linux/property.h>
> +
> +#define DISPLAY_SMB_REG 0x00
> +#define RGB_555_MASK 0x1f
> +#define NUM_LEDS 8
> +#define NUM_CHANNELS 3
> +
> +struct sensehat_display {
> +	struct platform_device *pdev;
> +	struct miscdevice mdev;
> +	struct mutex rw_mtx;

Calling this rw_mtx is misleading, since it is not a rw_mutex. We should
rename it to mtx.

> +	u8 vmem[NUM_LEDS][NUM_LEDS][NUM_CHANNELS];
> +	struct regmap *regmap;
> +};
> +
> +#define VMEM_SIZE sizeof_field(struct sensehat_display, vmem)
> +
> +
> +static int sensehat_update_display(struct sensehat_display *display)
> +{
> +	int i, j, k, ret;
> +	u8 buff[NUM_LEDS][NUM_CHANNELS][NUM_LEDS];
> +
> +	for (i = 0; i < NUM_LEDS; ++i)
> +		for (j = 0; j < NUM_LEDS; ++j)
> +			for (k = 0; k < NUM_CHANNELS; ++k)
> +				buff[i][k][j] =
> +					display->vmem[i][j][k] & RGB_555_MASK;
> +
> +	ret = regmap_bulk_write(display->regmap, DISPLAY_SMB_REG, buff,
> +				VMEM_SIZE);
> +	if (ret < 0)
> +		dev_err(&display->pdev->dev,
> +			"Update to 8x8 LED matrix display failed");
> +	return ret;
> +}
> +
> +static loff_t sensehat_display_llseek(struct file *filp, loff_t offset,
> +				      int whence)
> +{
> +	return fixed_size_llseek(filp, offset, whence, VMEM_SIZE);
> +}
> +
> +static ssize_t sensehat_display_read(struct file *filp, char __user *buf,
> +				     size_t count, loff_t *f_pos)
> +{
> +	struct sensehat_display *sensehat_display =
> +		container_of(filp->private_data, struct sensehat_display, mdev);
> +	ssize_t ret = -EFAULT;
> +
> +	if (*f_pos < 0 || *f_pos >= VMEM_SIZE)
> +		return 0;

Maybe it should return -EINVAL?

> +	count = min_t(size_t, count, VMEM_SIZE - *f_pos);
> +
> +	if (mutex_lock_interruptible(&sensehat_display->rw_mtx))
> +		return -ERESTARTSYS;
> +	if (copy_to_user(buf, *f_pos + (u8 *)sensehat_display->vmem, count))
> +		goto out;
> +	*f_pos += count;
> +	ret = count;
> +out:
> +	mutex_unlock(&sensehat_display->rw_mtx);
> +	return ret;
> +}
> +
> +static ssize_t sensehat_display_write(struct file *filp, const char __user *buf,
> +				      size_t count, loff_t *f_pos)
> +{
> +	struct sensehat_display *sensehat_display =
> +		container_of(filp->private_data, struct sensehat_display, mdev);
> +	int ret = -EFAULT;
> +
> +	if (*f_pos < 0 || *f_pos >= VMEM_SIZE)
> +		return -EFBIG;
> +	count = min_t(size_t, count, VMEM_SIZE - *f_pos);
> +
> +	if (mutex_lock_interruptible(&sensehat_display->rw_mtx))
> +		return -ERESTARTSYS;
> +	if (copy_from_user(*f_pos + (u8 *)sensehat_display->vmem, buf, count))
> +		goto out;
> +	ret = sensehat_update_display(sensehat_display);
> +	if (ret < 0) {
> +		ret = -EIO;
> +		goto out;
> +	}
> +	*f_pos += count;
> +	ret = count;
> +out:
> +	mutex_unlock(&sensehat_display->rw_mtx);
> +	return ret;
> +}
> +
> +static const struct file_operations sensehat_display_fops = {
> +	.owner = THIS_MODULE,
> +	.llseek = sensehat_display_llseek,
> +	.read = sensehat_display_read,
> +	.write = sensehat_display_write,
> +};
> +
> +static int sensehat_display_probe(struct platform_device *pdev)
> +{
> +	int ret;
> +
> +	struct sensehat_display *sensehat_display =
> +		devm_kmalloc(&pdev->dev, sizeof(*sensehat_display), GFP_KERNEL);
> +	if (!sensehat_display)
> +		return -ENOMEM;
> +
> +	sensehat_display->pdev = pdev;
> +
> +	dev_set_drvdata(&pdev->dev, sensehat_display);
> +
> +	sensehat_display->regmap = dev_get_regmap(pdev->dev.parent, NULL);
> +	if (!sensehat_display->regmap) {
> +		dev_err(&pdev->dev,
> +			"unable to get sensehat regmap");
> +		return -ENODEV;
> +	}
> +
> +	memset(sensehat_display->vmem, 0, VMEM_SIZE);
> +
> +	mutex_init(&sensehat_display->rw_mtx);
> +
> +	ret = sensehat_update_display(sensehat_display);
> +	if (ret < 0) {
> +		dev_err(&pdev->dev,
> +			"Could not communicate with sensehat");
> +		return ret;
> +	}
> +
> +	sensehat_display->mdev = (struct miscdevice){
> +		.minor = MISC_DYNAMIC_MINOR,
> +		.name = "sense-hat",
> +		.mode = 0666,
> +		.fops = &sensehat_display_fops,
> +	};
> +
> +	ret = misc_register(&sensehat_display->mdev);
> +	if (ret < 0) {
> +		dev_err(&pdev->dev,
> +			"Could not register 8x8 LED matrix display.");
> +		return ret;
> +	}
> +
> +	dev_info(&pdev->dev,
> +		 "8x8 LED matrix display registered with minor number %i",
> +		 sensehat_display->mdev.minor);
> +
> +	return 0;
> +}
> +
> +static int sensehat_display_remove(struct platform_device *pdev)
> +{
> +	struct sensehat_display *sensehat_display = dev_get_drvdata(&pdev->dev);
> +
> +	misc_deregister(&sensehat_display->mdev);
> +	return 0;
> +}
> +
> +static const struct of_device_id sensehat_display_device_id[] = {
> +	{ .compatible = "raspberrypi,sensehat-display" },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, sensehat_display_device_id);
> +
> +static struct platform_driver sensehat_display_driver = {
> +	.probe = sensehat_display_probe,
> +	.remove = sensehat_display_remove,
> +	.driver = {
> +		.name = "sensehat-display",
> +		.of_match_table = sensehat_display_device_id,
> +	},
> +};
> +
> +module_platform_driver(sensehat_display_driver);
> +
> +MODULE_DESCRIPTION("Raspberry Pi Sense HAT 8x8 LED matrix display driver");
> +MODULE_AUTHOR("Charles Mirabile <cmirabil@redhat.com>");
> +MODULE_AUTHOR("Serge Schneider <serge@raspberrypi.org>");
> +MODULE_LICENSE("GPL");
> -- 
> 2.31.1
> 
>