Re: [PATCH 3/5] irqchip/qcom-pdc: Configure PDC to pass through mode

["Maulik Shah (mkshah)" <maulik.shah@oss.qualcomm.com>]

On 3/13/2026 5:19 PM, Konrad Dybcio wrote:
> On 3/13/26 7:40 AM, Maulik Shah (mkshah) wrote:
>>
>>
>> On 3/13/2026 7:52 AM, Dmitry Baryshkov wrote:
>>> On Thu, Mar 12, 2026 at 09:26:37PM +0530, Maulik Shah wrote:
> 
> [...]
> 
>>>> All the SoCs so far default uses pass through mode with the exception of
>>>
>>> Is it something that must be configured by the bootloaders?
>>
>> yes, currently changing the the mode can be done from secure world either at boot
>> or after boot via scm write.
> 
> ..which won't work on almost any X1E devices, except CRD and IOT..

The series "works" for all x1e devices with added SS3 low power mode and GPIO
interrupts also continue to work for all.

> 
>>>> x1e. x1e PDC may be set to secondary controller mode for builds on CRD
>>>> boards whereas it may be set to pass through mode for IoT-EVK.
>>>>
>>>> There is no way to read which current mode it is set to and make PDC work
>>>> in respective mode as the read access is not opened up for non secure
>>>> world. There is though write access opened up via SCM write API to set the
>>>> mode.
>>>
>>> What are going to loose? The ability to latch the wakeup sources on the
>>> CRD?
>>
>> CXPC (SoC level low power mode) would be lost if the device can not wake up from GPIO wakeup sources.
> 
> To the best of my understanding, that's only because your approach chooses
> to ignore supporting the secondary controller mode and force-reconfigure,
> since GPIO wakeup functionality is otherwise available regardless of the
> mode.
> 

Yes, secondary controller mode was of no practical use in Linux and
hence the v1 series chosen to ignore it. This part is captured in the HDD
(hardware design document) too, 

"Some of SW platforms can’t detect all type of interrupts [..]
the ask is for the PDC to act as secondary interrupt controller [..]
Please note that not all SW platforms might enable and use this feature"

Linux did not have any problem working with all types of interrupts and
hence did not want to enable and carry this feature in Linux PDC irqchip.
This was added for specific windows SW platform requirement and was never
intended for Linux SW use.

Saying this, In v2 series adding the secondary mode support and with that
PDC irqchip driver will have capability to work in the secondary mode.

>>>> Configure PDC mode to pass through mode for all x1e based boards via SCM
>>>> write.
>>>
>>> Would it make sense to always use the secondary mode instead?
>>
>> No, it would not make sense to support the secondary mode in Linux.
> 
> Why?

Above reply covers same.

> 
> [...]
> 
>>>> +		 *	- Inform TLMM to monitor GPIO IRQs (same as MPM)
>>>> +		 *	- Prevent SoC low power mode (CxPC) as PDC is not
>>>> +		 *	  monitoring GPIO IRQs which may be needed to wake
>>>> +		 *	  the SoC from low power mode.
>>>
>>> This doesn't quite match the description of "latches the GPIO IRQs".
>>
>> It does, PDC would continue to still latch the GPIO IRQs (as the mode change failed)
>> but PDC won't forward them to parent GIC as they are masked at PDC with __pdc_mask_intr().
> 
> Can you not refrain from masking them then, and clear them upon reception,
> with a write to IRQ_i_CFG[IRQ_STATUS]?

This needs other changes too apart from clearing them upon reception.
They are part of v2 (to be sent).

> 
> The HPG states that this mechanism is only engaged for GPIO IRQs and that
> the forwarded interrupt will be of LEVEL_HIGH type (which is what TLMM
> accepts anyway)

TLMM isn't much used for IRQs which are routed via PDC.

Thanks,
Maulik