[U-Boot] [PATCH 2/4] serial: protect access to serial rx buffer

[Simon Glass]

On 3 August 2018 at 05:38, Patrick Delaunay <patrick.delaunay at st.com> wrote:
> Add test to avoid access to rx buffer when this buffer is empty.
> In this case directly call getc() function to avoid issue when tstc()
> is not called.
>
> Signed-off-by: Patrick Delaunay <patrick.delaunay at st.com>
> ---
>
>  drivers/serial/serial-uclass.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/serial/serial-uclass.c b/drivers/serial/serial-uclass.c
> index 321d23e..4121a37 100644
> --- a/drivers/serial/serial-uclass.c
> +++ b/drivers/serial/serial-uclass.c
> @@ -228,6 +228,9 @@ static int _serial_getc(struct udevice *dev)
>         struct serial_dev_priv *upriv = dev_get_uclass_priv(dev);
>         char val;
>
> +       if (upriv->rd_ptr == upriv->wr_ptr)
> +               return __serial_getc(dev);
> +
>         val = upriv->buf[upriv->rd_ptr++];
>         upriv->rd_ptr %= CONFIG_SERIAL_RX_BUFFER_SIZE;
>
> --
> 2.7.4
>

Reviewed-by: Simon Glass <sjg at chromium.org>

BTW I think the code in _serial_tstc() is wrong, or at least sub-optimal:

/* Read all available chars into the RX buffer */
while (__serial_tstc(dev)) {
   upriv->buf[upriv->wr_ptr++] = __serial_getc(dev);
   upriv->wr_ptr %= CONFIG_SERIAL_RX_BUFFER_SIZE;
}

It should call serial_getc() until it returns -EAGAIN. There should be
no need to call __serial_tstc() first,

Regards,
Simon