Re: [V2 PATCH 1/5] ACPI / scan: Parse _CCA and setup device coherency

Suravee Suthikulpanit
2015-05-06T04:15:53Z

[RESEND]

On 5/5/15 15:36, Rafael J. Wysocki wrote:
> On Tuesday, May 05, 2015 10:12:05 AM Suravee Suthikulpanit wrote:
>> diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
>> index ab2cbb5..dd386e9 100644
>> --- a/drivers/acpi/Kconfig
>> +++ b/drivers/acpi/Kconfig
>> @@ -54,6 +54,12 @@ config ACPI_GENERIC_GSI
>> config ACPI_SYSTEM_POWER_STATES_SUPPORT
>> bool
>>
>> +config ACPI_MUST_HAVE_CCA
>
> ACPI_CCA_REQUIRED maybe?

Sure.

>
>> + bool
>> +
>> +config ACPI_SUPPORT_CCA_ZERO
>
> I guess this means "we support devices that can DMA, but are not coherent".
> right?

Yes, basically when _CCA=0.

>> + bool
>> +
>> config ACPI_SLEEP
>> bool
>> depends on SUSPEND || HIBERNATION
>> diff --git a/drivers/acpi/acpi_platform.c b/drivers/acpi/acpi_platform.c
>> index 4bf7559..a6feca4 100644
>> --- a/drivers/acpi/acpi_platform.c
>> +++ b/drivers/acpi/acpi_platform.c
>> @@ -108,9 +108,11 @@ struct platform_device *acpi_create_platform_device(struct acpi_device *adev)
>> if (IS_ERR(pdev))
>> dev_err(&adev->dev, "platform device creation failed: %ld\n",
>> PTR_ERR(pdev));
>> - else
>> + else {
>
> Please add braces to both branches when making such changes (as per CodingStyle).
>

OK.

>> + acpi_setup_device_dma(adev, &pdev->dev);
>
> Why do we need to do that here (for the second time)?

Because we are calling:
acpi_create_platform_device()
|--> platform_device_register_device_full()
|-->platform_device_alloc()

This creates platform_device, which allocate a new platform_device->dev.
This is not the same as the original acpi_device->dev that was created
during acpi_add_single_object(). So, we have to set up the device
coherency again.

>> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
>> index 849b699..ac33b29 100644
>> --- a/drivers/acpi/scan.c
>> +++ b/drivers/acpi/scan.c
>> @@ -11,6 +11,7 @@
>> #include <linux/kthread.h>
>> #include <linux/dmi.h>
>> #include <linux/nls.h>
>> +#include <linux/dma-mapping.h>
>>
>> #include <asm/pgtable.h>
>>
>> @@ -2137,6 +2138,66 @@ void acpi_free_pnp_ids(struct acpi_device_pnp *pnp)
>> kfree(pnp->unique_id);
>> }
>>
>> +void acpi_setup_device_dma(struct acpi_device *adev, struct device *dev)
>> +{
>> + int coherent = acpi_dma_is_coherent(adev);
>> +
>> + /**
>> + * Currently, we only support DMA for devices that _CCA=1
>> + * since this seems to be the case on most ACPI platforms.
>> + *
>> + * For the case when _CCA=0 (i.e. is_coherent=0 && cca_seen=1),
>> + * we would rely on arch-specific cache maintenance for
>> + * non-coherence DMA operations if architecture enables
>> + * CONFIG_ACPI_SUPPORT_CCA_ZERO.
>> + *
>> + * For the case when _CCA is missing but platform requires it
>> + * (i.e. is_coherent=0 && cca_seen=0), we do not call
>> + * arch_setup_dma_ops() and fallback to arch-specific default
>> + * handling.
>> + */
>> + if (adev->flags.cca_seen) {
>> + if (!coherent && !IS_ENABLED(CONFIG_ACPI_SUPPORT_CCA_ZERO))
>> + return;
>> + arch_setup_dma_ops(dev, 0, 0, NULL, coherent);
>
> Oh dear.

I made a mistake here. This logic should also call arch_setup_dma_ops()
when cca_seen=0 and coherent=1 (e.g. when _CCA is not required and
default to coherent when it is missing). The current logic doesn't do that.

>
> What about
>
> if (adev->flags.cca_seen && (coherent || IS_ENABLED(CONFIG_ACPI_SUPPORT_CCA_ZERO)))
> arch_setup_dma_ops(dev, 0, 0, NULL, coherent);

What about:
if (coherent ||
(adev->flags.cca_seen &&
IS_ENABLED(CONFIG_ACPI_SUPPORT_CCA_ZERO))
arch_setup_dma_ops(dev, 0, 0, NULL, coherent);

> I wonder how this is going to affect x86/ia64 too?
>

This should not affect x86 since arch_setup_dma_ops() is currently not
implement for x86, and default to NOP (see include/linux/dma-mapping.h).
Also, on x86, _CCA is not required and default to 1 if missing.

Thanks,

Suravee