On Mon, Jan 15, 2018 at 10:58 AM, Sean Young <sean@xxxxxxxx> wrote:
> The Sasem Remote Controller has an LCD, which is connnected via usb.
> Multiple write reg or write data commands can be combined into one usb
> packet.
>
> The latency of usb is such that if we send commands one by one, we get
> very obvious tearing on the LCD.
>
> By adding a flush function, we can buffer all commands until either
> the usb packet is full or the lcd changes are complete.
>
> Signed-off-by: Sean Young <sean@xxxxxxxx>
> ---
> drivers/auxdisplay/charlcd.c | 6 ++++++
Cc'ing Arnd and Greg since this touches include/misc as well.
Miguel
> include/misc/charlcd.h | 1 +
> 2 files changed, 7 insertions(+)
>
> diff --git a/drivers/auxdisplay/charlcd.c b/drivers/auxdisplay/charlcd.c
> index 45ec5ce697c4..a16c72779722 100644
> --- a/drivers/auxdisplay/charlcd.c
> +++ b/drivers/auxdisplay/charlcd.c
> @@ -642,6 +642,9 @@ static ssize_t charlcd_write(struct file *file, const char __user *buf,
> charlcd_write_char(the_charlcd, c);
> }
>
> + if (the_charlcd->ops->flush)
> + the_charlcd->ops->flush(the_charlcd);
> +
> return tmp - buf;
> }
>
> @@ -703,6 +706,9 @@ static void charlcd_puts(struct charlcd *lcd, const char *s)
>
> charlcd_write_char(lcd, *tmp);
> }
> +
> + if (lcd->ops->flush)
> + lcd->ops->flush(lcd);
> }
>
> /* initialize the LCD driver */
> diff --git a/include/misc/charlcd.h b/include/misc/charlcd.h
> index 23f61850f363..ff8fd456018e 100644
> --- a/include/misc/charlcd.h
> +++ b/include/misc/charlcd.h
> @@ -32,6 +32,7 @@ struct charlcd_ops {
> void (*write_cmd_raw4)(struct charlcd *lcd, int cmd); /* 4-bit only */
> void (*clear_fast)(struct charlcd *lcd);
> void (*backlight)(struct charlcd *lcd, int on);
> + void (*flush)(struct charlcd *lcd);
> };
>
> struct charlcd *charlcd_alloc(unsigned int drvdata_size);
> --
> 2.14.3
>
