linux-kernel - Re: [PATCH v7 0/2] PCI: designware-ep: Fix DBI access before core init

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Date: Wed, 10 Jan 2024 08:41:37 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Niklas Cassel <Niklas.Cassel@....com>
Cc: Krzysztof Wilczyński <kw@...ux.com>,
	"jingoohan1@...il.com" <jingoohan1@...il.com>,
	"gustavo.pimentel@...opsys.com" <gustavo.pimentel@...opsys.com>,
	"lpieralisi@...nel.org" <lpieralisi@...nel.org>,
	"robh@...nel.org" <robh@...nel.org>,
	"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"quic_bjorande@...cinc.com" <quic_bjorande@...cinc.com>,
	"fancer.lancer@...il.com" <fancer.lancer@...il.com>,
	"vidyas@...dia.com" <vidyas@...dia.com>
Subject: Re: [PATCH v7 0/2] PCI: designware-ep: Fix DBI access before core
 init

On Tue, Jan 09, 2024 at 05:58:53PM +0000, Niklas Cassel wrote:
> On Sun, Jan 07, 2024 at 04:27:07PM +0900, Krzysztof Wilczyński wrote:
> > Hello,
> 
> Hello Krzysztof, Manivannan,
> 
> > 
> > > This series is the continuation of previous work by Vidya Sagar [1] to fix the
> > > issues related to accessing DBI register space before completing the core
> > > initialization in some EP platforms like Tegra194/234 and Qcom SM8450.
> > 
> > Applied to controller/dwc-ep, thank you!
> > 
> > [01/02] PCI: designware-ep: Fix DBI access before core init
> >         https://git.kernel.org/pci/pci/c/d3d13b00a2cf
> > [02/02] PCI: designware-ep: Move pci_epc_init_notify() inside dw_pcie_ep_init_complete()
> >         https://git.kernel.org/pci/pci/c/a171e1d60dad
> > 
> > 	Krzysztof
> 
> Considering that we know that this series introduces new problems
> for drivers with a .core_init_notifier (i.e. tegra and qcom), see:
> https://lore.kernel.org/linux-pci/ZWYmX8Y%2F7Q9WMxES@x1-carbon/
> 
> Do we really want to apply this series as is?
> 
> 

Niklas, I think I explained it in this thread itself. Let me reiterate here
again.

The fact that you are seeing the dmaengine warnings is due to function drivers
not releasing the channels properly. It is not the job of the DWC driver to
release the channels. The channels are requested by the function drivers [1]
and they _should_ release them when the channels are no longer required.

I know that the PCI_EPF_TEST driver is not doing so and so you are seeing the
warnings. But I do not have a device to test that function driver. Qcom
platforms use a dedicated function driver and that releases the channels when it
gets the LINK_DOWN event from EPC [2].

So my conclusion is that the issue is there even without this series. If you
still want me to fix the EPF_TEST driver, I can submit a change, but someone has
to test it.

- Mani

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pci/endpoint/functions/pci-epf-test.c#n229
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pci/endpoint/functions/pci-epf-mhi.c#n563

> Reading the patch, it appears that (at least some) tegra and
> qcom boards currently causes a whole system hang, which IIUC,
> renders those boards unusable.
> 
> So perhaps the new issues introduced by this series is preferable
> to a whole system hang.
> 
> As such, I can understand the urgency to merge this series.
> However, at the very least, I think that it might be worth amending
> the commit message to mention that this will currently not deregister
> the dma device in a clean way, leading to e.g. superfluous entries in
> /sys/class/dma/ and debugfs warnings being printed to dmesg.
> 
> 
> Kind regards,
> Niklas

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