Re: [PATCH v2] serial: 8250_dw: Avoid pslverr on reading empty receiver fifo

[Andy Shevchenko]

On Wed, Jul 13, 2022 at 2:43 PM Vamshi Gajjela <vamshigajjela@xxxxxxxxxx> wrote:
>
> From: VAMSHI GAJJELA <vamshigajjela@xxxxxxxxxx>
>
> With PSLVERR_RESP_EN parameter set to 1, the device generates an error
> response when an attempt to read an empty RBR with FIFO enabled.
>
> This happens when LCR writes are ignored when UART is busy.
> dw8250_check_lcr() in retries to update LCR, invokes dw8250_force_idle()
> to clear and reset FIFO and eventually reads UART_RX causing the error.
>
> Avoid this by not reading RBR/UART_RX when no data is available.

Thanks for an update!
My comments below.

...

> +       /*
> +        * With PSLVERR_RESP_EN parameter set to 1, the device generates an
> +        * error response when an attempt to read empty RBR with FIFO enabled.

an empty

> +        */
> +       lsr = p->serial_in(p, UART_LSR);

I have just noticed that you do it independently on FIFO enablement.

> +       if ((up->fcr & UART_FCR_ENABLE_FIFO) && !(lsr & UART_LSR_DR))
> +               return;

I would recommend to move it inside the conditional

  if (fcr & FIFO) {
    lsr = ...
    if (!(lsr &))
      return;
  }

-- 
With Best Regards,
Andy Shevchenko