Re: [PATCH v3 19/24] xen/8250-uart: add missing definitions

[Jan Beulich <jbeulich@xxxxxxxx>]

On 29.01.2025 02:16, Denis Mukhin wrote:
> On Tuesday, January 28th, 2025 at 2:34 PM, Jason Andryuk 
> <jason.andryuk@xxxxxxx> wrote:
> 
>>
>>
>> On 2025-01-03 20:58, Denis Mukhin via B4 Relay wrote:
>>
>>> From: Denis Mukhin dmukhin@xxxxxxxx
>>>
>>> Added missing definitions needed for NS8250 UART emulator.
>>>
>>> Re-used newly introduced MSR definitions in the existing ns16550 driver.
>>>
>>> Also, fixed indentation in a comment for FCR register.
>>>
>>> Signed-off-by: Denis Mukhin dmukhin@xxxxxxxx
>>> ---
>>> xen/drivers/char/ns16550.c | 6 ++--
>>> xen/include/xen/8250-uart.h | 78 
>>> +++++++++++++++++++++++++++++++++------------
>>> 2 files changed, 60 insertions(+), 24 deletions(-)
>>
>>> diff --git a/xen/include/xen/8250-uart.h b/xen/include/xen/8250-uart.h
>>> index 
>>> d13352940c13c50bac17d4cdf2f3bf584380776a..6d1af31d582a3dd674a401d7f649e28c889cdc3e
>>>  100644
>>> --- a/xen/include/xen/8250-uart.h
>>> +++ b/xen/include/xen/8250-uart.h
>>
>>> @@ -51,12 +54,19 @@
>>> #define UART_IIR_THR 0x02 /* - tx reg. empty /
>>> #define UART_IIR_MSI 0x00 / - MODEM status /
>>> #define UART_IIR_BSY 0x07 / - busy detect (DW) /
>>> +#define UART_IIR_FE 0xC0 / FIFO enabled (2 bits) */
>>>
>>> /* FIFO Control Register /
>>> -#define UART_FCR_ENABLE 0x01 / enable FIFO /
>>> -#define UART_FCR_CLRX 0x02 / clear Rx FIFO /
>>> -#define UART_FCR_CLTX 0x04 / clear Tx FIFO /
>>> -#define UART_FCR_DMA 0x10 / enter DMA mode */
>>
>>
>> 0x10 is bit 4...
>>
>>> +#define UART_FCR_ENABLE BIT(0, U) /* enable FIFO /
>>> +#define UART_FCR_CLRX BIT(1, U) / clear Rx FIFO /
>>> +#define UART_FCR_CLTX BIT(2, U) / clear Tx FIFO /
>>> +#define UART_FCR_DMA BIT(3, U) / enter DMA mode */
>>
>>
>> Now it's 0x08. Is this a bug fix? Looks like UART_FCR_DMA is unused.
> 
> Correct, NS16550 defines FCR DMA as bit#3 (0x08):
>   https://www.ti.com/lit/ds/symlink/tl16c550c.pdf
> 
>   Table 7-3. Summary of Accessible Registers
>   7.7.2 FIFO Control Register (FCR)

Any actual corrections you make need mentioning in the description.
I'm glad Jason spotted this; I did overlook it.

Jan