Re: [PATCH] wifi: ath12k: fix CMA error and MHI state mismatch during resume

[Baochen Qiang <baochen.qiang@oss.qualcomm.com>]

On 2/3/2026 1:02 PM, Jayasaikiran Banigallapati wrote:
> 
> On 2/3/26 08:21, Baochen Qiang wrote:
>>
>> On 2/2/2026 11:17 PM, Saikiran wrote:
>>> Commit 8d5f4da8d70b ("wifi: ath12k: support suspend/resume") introduced
>>> system suspend/resume support but caused a critical regression where
>>> CMA pages are corrupted during resume.
>>>
>>> 1. CMA page corruption:
>>>     Calling mhi_unprepare_after_power_down() during suspend (via
>>>     ATH12K_MHI_DEINIT) prematurely frees the fbc_image and rddm_image
>>>     DMA buffers. When these pages are accessed during resume, the kernel
>>>     detects corruption (Bad page state).
>> How, FBC image and RDDM image get re-allocated at resume, no?
>>
>> To clarify, the BUG: Bad page state crash actually occurs during the suspend phase,
>> specifically when ath12k_mhi_stop() calls mhi_unprepare_after_power_down().
>>
>> The stack trace shows the panic happens inside mhi_free_bhie_table() while trying to
>> free the pages:
>>
>>  mhi_free_bhie_table+0x50/0xa0 [mhi]
>>  mhi_unprepare_after_power_down+0x30/0x70 [mhi]
>>  ath12k_mhi_stop+0xf8/0x210 [ath12k]
>>  ath12k_core_suspend_late+0x94/0xc0 [ath12k]
>>
>> The kernel reports nonzero _refcount when attempting to free the CMA pages (fbc_image/
>> rddm_image). This suggests that something is still holding a reference to these pages
>> when DEINIT attempts to free them, causing the kernel to panic before we reach the
>> resume stage.

this seems like a bug either in MHI stack or in kernel DMA/MM subsystems, rather than in
ath12k

>>
>> Since the pages cannot be safely freed during suspend, skipping DEINIT (and using
>> MHI_POWER_OFF_KEEP_DEV) avoids this invalid free operation. This also aligns with the
>> existing comment in ath12k_mhi_stop which suggests using mhi_power_down_keep_dev() for
>> suspend.

first of all, this is a workaround rather than fix. Ideally we should try to root cause
the issue and fix it in the right way.

Secondly the workaround here seems problematic: you skip INIT druing resume. However note
several hardware registers need to be re-programmed during this stage, how could the
target work if its power is cutoff during suspend and the register context is not restored
during resume?

>>
>> Thanks & Regards,
>> Saikiran