Re: [PATCH v3 5/5] hw/char/pl011: check if UART is enabled before RX or TX operation

[Evgeny Iakovlev <eiakovlev@linux.microsoft.com>]

On 1/23/2023 09:14, Philippe Mathieu-Daudé wrote:
> On 20/1/23 16:54, Evgeny Iakovlev wrote:
>> UART should be enabled in general and have RX enabled specifically to be
>> able to receive data from peripheral device. Same goes for transmitting
>> data to peripheral device and a TXE flag.
>>
>> Check if UART CR register has EN and RXE or TXE bits enabled before
>> trying to receive or transmit data.
>>
>> Signed-off-by: Evgeny Iakovlev <eiakovlev@linux.microsoft.com>
>> Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
>> ---
>>   hw/char/pl011.c | 22 +++++++++++++++++++---
>>   1 file changed, 19 insertions(+), 3 deletions(-)
>
>> +static inline bool pl011_can_transmit(PL011State *s)
>> +{
>> +    return s->cr & PL011_CR_UARTEN && s->cr & PL011_CR_TXE;
>> +}
>> +
>>   static void pl011_write(void *opaque, hwaddr offset,
>>                           uint64_t value, unsigned size)
>>   {
>> @@ -221,7 +231,9 @@ static void pl011_write(void *opaque, hwaddr offset,
>>         switch (offset >> 2) {
>>       case 0: /* UARTDR */
>> -        /* ??? Check if transmitter is enabled.  */
>> +        if (!pl011_can_transmit(s)) {
>> +            break;
>> +        }
>>           ch = value;
>>           /* XXX this blocks entire thread. Rewrite to use
>>            * qemu_chr_fe_write and background I/O callbacks */
>> @@ -292,7 +304,11 @@ static int pl011_can_receive(void *opaque)
>>       PL011State *s = (PL011State *)opaque;
>>       int r;
>>   -    r = s->read_count < pl011_get_fifo_depth(s);
>> +    if (!(s->cr & PL011_CR_UARTEN) || !(s->cr & PL011_CR_RXE)) {
>
> Maybe add pl011_can_receive() similarly to pl011_can_transmit().
>
> Otherwise:
> Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>


Thanks! There's already a pl011_can_receive though, its the 
pl011_can_transmit that's new :)


>
>> +        r = 0;
>> +    } else {
>> +        r = s->read_count < pl011_get_fifo_depth(s);
>> +    }
>>       trace_pl011_can_receive(s->lcr, s->read_count, r);
>>       return r;
>>   }