Re: [Xen-devel] [PATCH v4] ns16550: Add ACPI support for ARM only

[Jan Beulich <jbeulich@xxxxxxxx>]

On 24.02.2020 02:06, Wei Xu wrote:
> On 2020/2/21 23:07, Jan Beulich wrote:
>> On 21.02.2020 15:57, Julien Grall wrote:
>>> On 21/02/2020 14:02, Jan Beulich wrote:
>>>> On 21.02.2020 03:22, Wei Xu wrote:
>>>>> --- a/xen/drivers/char/ns16550.c
>>>>> +++ b/xen/drivers/char/ns16550.c
>>>>> @@ -1620,6 +1620,85 @@ DT_DEVICE_START(ns16550, "NS16550 UART", 
>>>>> DEVICE_SERIAL)
>>>>>   DT_DEVICE_END
>>>>>
>>>>>   #endif /* HAS_DEVICE_TREE */
>>>>> +
>>>>> +#if defined(CONFIG_ACPI) && defined(CONFIG_ARM)
>>>>> +#include <xen/acpi.h>
>>>>> +
>>>>> +static int __init ns16550_acpi_uart_init(const void *data)
>>>>> +{
>>>>> +    struct acpi_table_header *table;
>>>>> +    struct acpi_table_spcr *spcr;
>>>>> +    acpi_status status;
>>>>> +    /*
>>>>> +     * Same as the DT part.
>>>>> +     * Only support one UART on ARM which happen to be ns16550_com[0].
>>>>> +     */
>>>>> +    struct ns16550 *uart = &ns16550_com[0];
>>>>> +
>>>>> +    status = acpi_get_table(ACPI_SIG_SPCR, 0, &table);
>>>>> +    if ( ACPI_FAILURE(status) )
>>>>> +    {
>>>>> +        printk("ns16550: Failed to get SPCR table\n");
>>>>> +        return -EINVAL;
>>>>> +    }
>>>>> +
>>>>> +    spcr = container_of(table, struct acpi_table_spcr, header);
>>>>> +
>>>>> +    /*
>>>>> +     * The serial port address may be 0 for example
>>>>> +     * if the console redirection is disabled.
>>>>> +     */
>>>>> +    if ( unlikely(!spcr->serial_port.address) )
>>>>> +    {
>>>>> +        printk("ns16550: Console redirection is disabled\n");
>>>>> +        return -EINVAL;
>>>>> +    }
>>>>> +
>>>>> +    if ( unlikely(spcr->serial_port.space_id != 
>>>>> ACPI_ADR_SPACE_SYSTEM_MEMORY) )
>>>>> +    {
>>>>> +        printk("ns16550: Address space type is not mmio\n");
>>>>> +        return -EINVAL;
>>>>> +    }
>>>>
>>>> The space_id field qualifies the address one, i.e. whether a value of
>>>> zero can sensibly mean "disabled" depends on the address space. Hence
>>>> logically the address space check should come first.
>>>>
>>>> This is the last thing I'd like to see changed. I won't give the
>>>> patch my ack though, as I think it should be an Arm maintainer to ack
>>>> it.
>>>
>>> Acked-by: Julien Grall <julien@xxxxxxx>
>>>
>>> Although, a reviewed-by tag from you would be nice as you did most of 
>>> the review for this patch.
>>
>> Well, to clarify - this is one of the very few (afaict) cases where our
>> R-b implying A-b (when people are entitled to ack the respective code)
>> gets in the way. If this wasn't the case, I'd have given the former,
>> making it clear (also later from just looking at the resulting commit)
>> that the (only) ack came from an Arm person.
> 
> I will check the address space in the v5 and add your R-b.

I guess some misunderstanding has occurred? You're already checking the
address space in v4 (and I did already commit it this way on Friday).
And as indicated I intentionally elected to not provide my R-b for this
patch, for the reason given above.

Jan

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