Re: [PATCH] Revert "hw/char/pl011: Warn when using disabled receiver"

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 12/3/25 14:43, Peter Maydell wrote:
> On Wed, 12 Mar 2025 at 13:36, Peter Maydell <peter.maydell@linaro.org> wrote:
>>
>> On Tue, 11 Mar 2025 at 15:37, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>>
>>> The guest does not control whether characters are sent on the UART.
>>> Sending them before the guest happens to boot will now result in a
>>> "guest error" log entry that is only because of timing, even if the
>>> guest _would_ later setup the receiver correctly.
>>>
>>> This reverts commit abf2b6a028670bd2890bb3aee7e103fe53e4b0df, apart
>>> from adding the comment.
>>>
>>> Cc: Philippe Mathieu-Daudé <philmd@linaro.org>
>>> Cc: Peter Maydell <peter.maydell@linaro.org>
>>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>>> ---
>>>   hw/char/pl011.c | 12 ++----------
>>>   1 file changed, 2 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/hw/char/pl011.c b/hw/char/pl011.c
>>> index 23a9db8c57c..efca8baecd7 100644
>>> --- a/hw/char/pl011.c
>>> +++ b/hw/char/pl011.c
>>> @@ -85,7 +85,6 @@ DeviceState *pl011_create(hwaddr addr, qemu_irq irq, Chardev *chr)
>>>   #define CR_OUT1     (1 << 12)
>>>   #define CR_RTS      (1 << 11)
>>>   #define CR_DTR      (1 << 10)
>>> -#define CR_RXE      (1 << 9)
>>>   #define CR_TXE      (1 << 8)
>>>   #define CR_LBE      (1 << 7)
>>>   #define CR_UARTEN   (1 << 0)
>>> @@ -490,16 +489,9 @@ static int pl011_can_receive(void *opaque)
>>>       unsigned fifo_depth = pl011_get_fifo_depth(s);
>>>       unsigned fifo_available = fifo_depth - s->read_count;
>>>
>>> -    if (!(s->cr & CR_UARTEN)) {
>>> -        qemu_log_mask(LOG_GUEST_ERROR,
>>> -                      "PL011 receiving data on disabled UART\n");
>>> -    }
>>> -    if (!(s->cr & CR_RXE)) {
>>> -        qemu_log_mask(LOG_GUEST_ERROR,
>>> -                      "PL011 receiving data on disabled RX UART\n");
>>> -    }
>>> +    /* Should check enable and return 0? */
>>
>> We decided deliberately not to check the enable and return 0
>> here, as described in the commit message of abf2b6a028670bd:
>> we think there's too likely to be existing works-on-QEMU code
>> out there that doesn't ever set the enable bits.
>>
>> Otherwise, yes, agreed with the revert.
> 
> Oh, and I just realized that the right place to diagnose
> "guest didn't enable the UART" would be when it reads/writes
> the data register while the enable bits are clear.

Doh, sorry. I wonder how I ended putting this code here... Since I
rebased this a lot, maybe something went wrong. Anyway, I'll post
a fix.

Regards,

Phil.