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 10:01:08 +0000
From: Niklas Cassel <Niklas.Cassel@....com>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
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

Hello Mani,

On Wed, Jan 10, 2024 at 08:41:37AM +0530, Manivannan Sadhasivam wrote:
> 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:
> > 
> > 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.

Sure, the function driver should release the channels.


> 
> 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.

That conclusion is not fully correct.

Let's take e.g. these error messages that this series introduces:
[ 1000.714355] debugfs: File 'mf' in directory '/' already present!
[ 1000.714890] debugfs: File 'wr_ch_cnt' in directory '/' already present!
[ 1000.715476] debugfs: File 'rd_ch_cnt' in directory '/' already present!
[ 1000.716061] debugfs: Directory 'registers' with parent '/' already present!

These come from dw_edma_core_debugfs_on(), which is called by dw_edma_probe().

This is a direct result from your patch:
https://git.kernel.org/pub/scm/linux/kernel/git/pci/pci.git/commit/?h=controller/dwc-ep&id=9ab5c8bb7a305135b1b6c65cb8db92b4acbef79d

Which moves dw_pcie_edma_detect() from dw_pcie_ep_init_complete() to
dw_pcie_ep_late_init() (since dw_pcie_edma_detect() calls dw_edma_probe()).

So without your patch, those debugfs error messages are not seen.

Thus, I do not think that it is sufficient to only modify the pci-epf-test
driver to release the dma channels, as I don't see how that will avoid e.g.
the debugfs error messages introduced by this patch.


Kind regards,
Niklas