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

From: Andy Shevchenko
Date: Tue Jul 12 2022 - 09:26:40 EST


On Tue, Jul 12, 2022 at 3:16 PM Vamshi Gajjela <vamshigajjela@xxxxxxxxxx> wrote:
>
> From: VAMSHI GAJJELA <vamshigajjela@xxxxxxxxxx>
>
> With PSLVERR_RESP_EN parameter set to 1, device generates an error

the device

> response when an attempt to read empty RBR with FIFO enabled.

an empty

> This happens when LCR writes are ignored when UART is busy.
> dw8250_check_lcr() in retries to updateLCR, invokes dw8250_force_idle()
> to clear and reset fifo and eventually reads UART_RX causing pslverr.

fifo --> FIFO
pslverr --> the error

> Avoid this by not reading RBR/UART_RX when no data is available.

...

> + unsigned int lsr;
> struct uart_8250_port *up = up_to_u8250p(p);

Can we keep it ordered according to the reversed xmas tree?

...

> + /*
> + * With PSLVERR_RESP_EN parameter set to 1, device generates pslverr

the device
pslverr --> an

> + * error response when an attempt to read empty RBR with FIFO enabled

Missed period.

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

The only caller of this function already has the lsr value, why you
can't (re)use it?

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

--
With Best Regards,
Andy Shevchenko