Re: [PATCH 3/5] drivers/auxdisplay: senshat: Raspberry Pi Sense HAT display driver

Matthias Brugger
2021-11-03T16:47:46Z

On 29/10/2021 23:55, Charles Mirabile wrote:
> This patch implements control of the 8x8 RGB LED matrix display.
>
> Signed-off-by: Charles Mirabile <cmirabil@redhat.com>
> Signed-off-by: Mwesigwa Guma <mguma@redhat.com>
> Signed-off-by: Joel Savitz <jsavitz@redhat.com>
> ---
> drivers/auxdisplay/Kconfig | 7 +
> drivers/auxdisplay/Makefile | 1 +
> drivers/auxdisplay/sensehat-display.c | 258 ++++++++++++++++++++++++++
> 3 files changed, 266 insertions(+)
> create mode 100644 drivers/auxdisplay/sensehat-display.c
>
[....]
> diff --git a/drivers/auxdisplay/sensehat-display.c b/drivers/auxdisplay/sensehat-display.c
> new file mode 100644
> index 000000000000..5980ad23fd4f
> --- /dev/null
> +++ b/drivers/auxdisplay/sensehat-display.c
[...]
> +
> +static ssize_t
> +sensehat_display_write(struct file *filp, const char __user *buf, size_t count, loff_t *f_pos)
> +{
> + struct sensehat *sensehat = container_of(filp->private_data, struct sensehat, display.mdev);
> + struct sensehat_display *sensehat_display = &sensehat->display;
> + u8 temp[VMEM_SIZE];
> +
> + if (*f_pos >= VMEM_SIZE)
> + return -EFBIG;
> + if (*f_pos + count > VMEM_SIZE)
> + count = VMEM_SIZE - *f_pos;
> + if (copy_from_user(temp, buf, count))
> + return -EFAULT;
> + if (mutex_lock_interruptible(&sensehat_display->rw_mtx))
> + return -ERESTARTSYS;
> + memcpy(sensehat_display->vmem + *f_pos, temp, count);

So we copy from buf into temp, from temp into vmem and then we 'transform' vmem
into the representation of pixel_data.

As you are implementing the user-space interface, couldn't we just change the
pixel representation there and get rid of the transformation?

> + sensehat_update_display(sensehat);
> + *f_pos += count;
> + mutex_unlock(&sensehat_display->rw_mtx);
> + return count;
> +}
> +
> +static long sensehat_display_ioctl(struct file *filp, unsigned int cmd,
> + unsigned long arg)
> +{
> + struct sensehat *sensehat = container_of(filp->private_data, struct sensehat, display.mdev);
> + struct sensehat_display *sensehat_display = &sensehat->display;
> + void __user *user_ptr = (void __user *)arg;
> + u8 temp[GAMMA_SIZE];
> + int ret;
> +
> + if (mutex_lock_interruptible(&sensehat_display->rw_mtx))
> + return -ERESTARTSYS;
> + switch (cmd) {
> + case SENSEDISP_IOGET_GAMMA:
> + if (copy_to_user(user_ptr, sensehat_display->gamma, GAMMA_SIZE)) {
> + ret = -EFAULT;
> + goto out_unlock;
> + }
> + ret = 0;
> + goto out_unlock;
> + case SENSEDISP_IOSET_GAMMA:
> + if (copy_from_user(temp, user_ptr, GAMMA_SIZE)) {
> + ret = -EFAULT;
> + goto out_unlock;
> + }
> + ret = 0;
> + goto out_update;

That's just a 'break;' correct?

Regards,
Matthias