Re: [PATCH v20 13/17] acpi/arm64: Add GTDT table parse driver

[Fu Wei]

Hi Hanjun,

On 19 January 2017 at 17:11, Hanjun Guo <hanjun.guo@xxxxxxxxxx> wrote:
> On 2017/1/18 21:25, fu.wei@xxxxxxxxxx wrote:
>>
>> From: Fu Wei <fu.wei@xxxxxxxxxx>
>>
>> This patch adds support for parsing arch timer info in GTDT,
>> provides some kernel APIs to parse all the PPIs and
>> always-on info in GTDT and export them.
>>
>> By this driver, we can simplify arm_arch_timer drivers, and
>> separate the ACPI GTDT knowledge from it.
>>
>> Signed-off-by: Fu Wei <fu.wei@xxxxxxxxxx>
>> Signed-off-by: Hanjun Guo <hanjun.guo@xxxxxxxxxx>
>> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>> Tested-by: Xiongfeng Wang <wangxiongfeng2@xxxxxxxxxx>
>> ---
>>  arch/arm64/Kconfig          |   1 +
>>  drivers/acpi/arm64/Kconfig  |   3 +
>>  drivers/acpi/arm64/Makefile |   1 +
>>  drivers/acpi/arm64/gtdt.c   | 157
>> ++++++++++++++++++++++++++++++++++++++++++++
>>  include/linux/acpi.h        |   6 ++
>>  5 files changed, 168 insertions(+)
>>
>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>> index 1117421..ab1ee10 100644
>> --- a/arch/arm64/Kconfig
>> +++ b/arch/arm64/Kconfig
>> @@ -2,6 +2,7 @@ config ARM64
>>         def_bool y
>>         select ACPI_CCA_REQUIRED if ACPI
>>         select ACPI_GENERIC_GSI if ACPI
>> +       select ACPI_GTDT if ACPI
>>         select ACPI_REDUCED_HARDWARE_ONLY if ACPI
>>         select ACPI_MCFG if ACPI
>>         select ACPI_SPCR_TABLE if ACPI
>> diff --git a/drivers/acpi/arm64/Kconfig b/drivers/acpi/arm64/Kconfig
>> index 4616da4..5a6f80f 100644
>> --- a/drivers/acpi/arm64/Kconfig
>> +++ b/drivers/acpi/arm64/Kconfig
>> @@ -4,3 +4,6 @@
>>
>>  config ACPI_IORT
>>         bool
>> +
>> +config ACPI_GTDT
>> +       bool
>> diff --git a/drivers/acpi/arm64/Makefile b/drivers/acpi/arm64/Makefile
>> index 72331f2..1017def 100644
>> --- a/drivers/acpi/arm64/Makefile
>> +++ b/drivers/acpi/arm64/Makefile
>> @@ -1 +1,2 @@
>>  obj-$(CONFIG_ACPI_IORT)        += iort.o
>> +obj-$(CONFIG_ACPI_GTDT)        += gtdt.o
>> diff --git a/drivers/acpi/arm64/gtdt.c b/drivers/acpi/arm64/gtdt.c
>> new file mode 100644
>> index 0000000..d93a790
>> --- /dev/null
>> +++ b/drivers/acpi/arm64/gtdt.c
>> @@ -0,0 +1,157 @@
>
> [...]
>
>> +
>> +/**
>> + * acpi_gtdt_init() - Get the info of GTDT table to prepare for further
>> init.
>> + * @table:     The pointer to GTDT table.
>> + * @platform_timer_count:      The pointer of int variate for returning
>> the
>> + *                             number of platform timers. It can be NULL,
>> if
>> + *                             driver don't need this info.
>> + *
>> + * Return: 0 if success, -EINVAL if error.
>> + */
>> +int __init acpi_gtdt_init(struct acpi_table_header *table,
>> +                         int *platform_timer_count)
>> +{
>> +       int ret = 0;
>> +       int timer_count = 0;
>> +       void *platform_timer = NULL;
>> +       struct acpi_table_gtdt *gtdt;
>> +
>> +       gtdt = container_of(table, struct acpi_table_gtdt, header);
>> +       acpi_gtdt_desc.gtdt = gtdt;
>> +       acpi_gtdt_desc.gtdt_end = (void *)table + table->length;
>> +
>> +       if (table->revision < 2)
>> +               pr_debug("Revision:%d doesn't support Platform Timers.\n",
>> +                        table->revision);
>
>
> GTDT table revision is updated to 2 in ACPI 5.1, we will
> not support ACPI version under 5.1 and disable ACPI in FADT
> parse before this code is called, so if we get revision
> <2 here, I think we need to print warning (we need to keep
> the firmware stick to the spec on ARM64).

agree, will change pr_debug to pr_warn.

Thanks :-)

>
>> +       else if (!gtdt->platform_timer_count)
>> +               pr_debug("No Platform Timer.\n");
>> +       else
>> +               timer_count = gtdt->platform_timer_count;
>> +
>> +       if (timer_count) {
>> +               platform_timer = (void *)gtdt +
>> gtdt->platform_timer_offset;
>> +               if (platform_timer < (void *)table +
>> +                                    sizeof(struct acpi_table_gtdt)) {
>> +                       pr_err(FW_BUG "invalid timer data.\n");
>
>
> It's ok but I didn't see other ACPI tables parsing did this check,
> maybe we can just remove it :)

here, I want to make sure the FW is valid.
Once there is a FW bug, we could just return with error.  :-)

>
>> +                       timer_count = 0;
>> +                       platform_timer = NULL;
>> +                       ret = -EINVAL;
>> +               }
>> +       }
>> +
>> +       acpi_gtdt_desc.platform_timer = platform_timer;
>> +       if (platform_timer_count)
>> +               *platform_timer_count = timer_count;
>
>
> Then the code will much simple:
>
> if (gtdt->platform_timer_count) {
>         acpi_gtdt_desc.platform_timer = (void *)gtdt +
> gtdt->platform_timer_offset;
>         if (platform_timer_count)
>                 *platform_timer_count = gtdt->platform_timer_count;
> }
>
> return 0;
>
> and remove ret, timer_count and platform_timer.

yes, this may can simplify the function, but this will be released at
the end of init because of "__init" :-)
So how about let's just keep this check to make sure the FW is OK.  :-)

>
> Thanks
> Hanjun



-- 
Best regards,

Fu Wei
Software Engineer
Red Hat