Re: [PATCH v2 1/2] acpi, spcr: Make SPCR avialable to other architectures

Timur Tabi
2017-12-13T21:11:43Z

On 12/13/2017 06:45 AM, Lorenzo Pieralisi wrote:
>> +/*
>> + * Erratum 44 for QDF2432v1 and QDF2400v1 SoCs describes the BUSY bit as
>> + * occasionally getting stuck as 1. To avoid the potential for a hang, check
>> + * TXFE == 0 instead of BUSY == 1. This may not be suitable for all UART
>> + * implementations, so only do so if an affected platform is detected in
>> + * acpi_parse_spcr().
>> + */
>> +bool qdf2400_e44_present;
>> +EXPORT_SYMBOL(qdf2400_e44_present);
>
> My eyes, this is horrible but it is not introduced by this patch. It
> would have been much better if:
>
> drivers/tty/serial/amba-pl011.c
>
> parsed the SPCR table (again) to detect it instead of relying on this
> horrible exported flag.

I didn't want to put any ACPI code in amba-pl011.c, so putting it in
spcr.c made the most sense. I agree the global variable is ugly. If
you have a better idea, I'm all ears.

If it's any consolation, this erratum affects only 1.x silicon, which is
technically pre-production (although a lot of people have them). This
work-around will eventually be reverted.

>> diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
>> index 46505396869e..9ae98eeada76 100644
>> --- a/drivers/acpi/Kconfig
>> +++ b/drivers/acpi/Kconfig
>> @@ -79,7 +79,12 @@ config ACPI_DEBUGGER_USER
>> endif
>>
>> config ACPI_SPCR_TABLE
>> - bool
>> + bool "ACPI Serial Port Console Redirection Support"
>> + default y if ARM64
>
> You need to remove the selection in arch/arm64 then. Also, moving away
> from a non-visible config may have consequences on ARM64, Graeme and
> Mark are more familiar with the SPCR dependencies so please chime in.

I did raise this as a concern in the previous version of the patch. I
also think it should not be a selectable option.

Keeping the "select" does force SPCR to be enabled on ARM64 ACPI
platforms, but if it's an option for x86, it should be an option for ARM.

--
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm
Technologies, Inc. Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.