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

[Jan Beulich <jbeulich@xxxxxxxx>]

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.

Jan

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