Re: [PATCH v2] bus: mhi: host: don't free bhie tables during suspend/hibernation

[Manivannan Sadhasivam]

On Fri, Apr 25, 2025 at 12:42:38PM +0500, Muhammad Usama Anjum wrote:
> On 4/25/25 12:32 PM, Manivannan Sadhasivam wrote:
> > On Fri, Apr 25, 2025 at 12:14:39PM +0500, Muhammad Usama Anjum wrote:
> >> On 4/25/25 12:04 PM, Manivannan Sadhasivam wrote:
> >>> On Thu, Apr 10, 2025 at 07:56:54PM +0500, Muhammad Usama Anjum wrote:
> >>>> Fix dma_direct_alloc() failure at resume time during bhie_table
> >>>> allocation. There is a crash report where at resume time, the memory
> >>>> from the dma doesn't get allocated and MHI fails to re-initialize.
> >>>> There may be fragmentation of some kind which fails the allocation
> >>>> call.
> >>>>
> >>>
> >>> If dma_direct_alloc() fails, then it is a platform limitation/issue. We cannot
> >>> workaround that in the device drivers. What is the guarantee that other drivers
> >>> will also continue to work? Will you go ahead and patch all of them which
> >>> release memory during suspend?
> >>>
> >>> Please investigate why the allocation fails. Even this is not a device issue, so
> >>> we cannot add quirks :/
> >> This isn't a platform specific quirk. We are only hitting it because
> >> there is high memory pressure during suspend/resume. This dma allocation
> >> failure can happen with memory pressure on any device.
> >>
> > 
> > Yes.
> Thanks for understanding.
> 
> > 
> >> The purpose of this patch is just to make driver more robust to memory
> >> pressure during resume.
> >>
> >> I'm not sure about MHI. But other drivers already have such patches as
> >> dma_direct_alloc() is susceptible to failures when memory pressure is
> >> high. This patch was motivated from ath12k [1] and ath11k [2].
> >>
> > 
> > Even if we patch the MHI driver, the issue is going to trip some other driver.
> > How does the DMA memory goes low during resume? So some other driver is
> > consuming more than it did during probe()?
> Think it like this. The first probe happens just after boot. Most of the
> RAM was empty. Then let's say user launches applications which not only
> consume entire RAM but also the Swap. The DMA memory area is the first
> ~4GB on x86_64 (if I'm not mistaken). Now at resume time when we want to
> allocate memory from dma, it may not be available entirely or because of
> fragmentation we cannot allocate that much contiguous memory.
> 

Looks like you have a workload that consumes the limited DMA coherent memory.
Most likely the GPU applications I think.

> In our testing and real world cases, right now only wifi driver is
> misbehaving. Wifi is also very important. So we are hoping to make wifi
> driver robust.
> 

Sounds fair. If you want to move forward, please modify the exisiting
mhi_power_down_keep_dev() to include this partial unprepare as well:

mhi_power_down_unprepare_keep_dev()

Since both APIs are anyway going to be used together, I don't see a need to
introduce yet another API.

- Mani

> > 
> >> [1]
> >> https://lore.kernel.org/all/20240419034034.2842-1-quic_bqiang@xxxxxxxxxxx/
> >> [2]
> >> https://lore.kernel.org/all/20220506141448.10340-1-quic_akolli@xxxxxxxxxxx/
> >>
> >> What do you think can be the way forward for this patch?
> >>
> > 
> > Let's try first to analyze why the memory pressure happens during suspend. As I
> > can see, even if we fix the MHI driver, you are likely to hit this issue
> > somewhere else.>
> > - Mani
> > 
> >>>
> > 
> > [...]
> > 
> >>> Did you intend to leak this information? If not, please remove it from
> >>> stacktrace.
> >> The device isn't private. Its fine.
> >>
> > 
> > Okay.
> > 
> > - Mani
> > 
> 
> 
> -- 
> Regards,
> Usama

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