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SubjectRe: [PATCH v2] serial: 8250_dw: Avoid pslverr on reading empty receiver fifo
On Wed, Jul 13, 2022 at 2:43 PM Vamshi Gajjela <vamshigajjela@google.com> wrote:
>
> From: VAMSHI GAJJELA <vamshigajjela@google.com>
>
> 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

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