linux-kernel - Re: [PATCH v7 2/2] PCI: keystone: Fix pci

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Message-ID: <20240516141742.GA2204499@bhelgaas>
Date: Thu, 16 May 2024 09:17:42 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Siddharth Vadapalli <s-vadapalli@...com>
Cc: lpieralisi@...nel.org, kw@...ux.com, robh@...nel.org,
	bhelgaas@...gle.com, manivannan.sadhasivam@...aro.org,
	fancer.lancer@...il.com, u.kleine-koenig@...gutronix.de,
	cassel@...nel.org, dlemoal@...nel.org,
	yoshihiro.shimoda.uh@...esas.com, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	srk@...com
Subject: Re: [PATCH v7 2/2] PCI: keystone: Fix pci_ops for AM654x SoC

On Thu, May 16, 2024 at 11:07:27AM +0530, Siddharth Vadapalli wrote:
> On Wed, May 15, 2024 at 02:26:14PM -0500, Bjorn Helgaas wrote:
> > On Tue, May 14, 2024 at 04:14:54PM -0500, Bjorn Helgaas wrote:
> > > On Tue, May 14, 2024 at 05:41:48PM +0530, Siddharth Vadapalli wrote:
> > > > On Mon, May 13, 2024 at 04:53:50PM -0500, Bjorn Helgaas wrote:
> > > ...
> > 
> > > > > I'm not quite clear on the mechanism, but it would be helpful to at
> > > > > least know what's wrong and on what platform.  E.g., currently v4.90
> > > > > suffers Completion Timeouts and 45 second boot delays?  And this patch
> > > > > fixes that?
> > > > 
> > > > Yes, the Completion Timeouts cause the 45 second boot delays and this
> > > > patch fixes that.
> > > 
> > > And this problem happens on AM654x/v4.90a, right?  I really want the
> > > commit log to say what platform is affected!
> > > 
> > > Maybe something like this?
> > > 
> > >   PCI: keystone: Enable BAR 0 only for v3.65a
> > > 
> > >   The BAR 0 initialization done by ks_pcie_v3_65_add_bus() should
> > >   happen for v3.65a devices only.  On other devices, BAR 0 should be
> > >   left disabled, as it is by dw_pcie_setup_rc().
> > > 
> > >   After 6ab15b5e7057 ("PCI: dwc: keystone: Convert .scan_bus()
> > >   callback to use add_bus"), ks_pcie_v3_65_add_bus() enabled BAR 0 for
> > >   both v3.65a and v4.90a devices.  On the AM654x SoC, which uses
> > >   v4.90a, enabling BAR 0 causes Completion Timeouts when setting up
> > >   MSI-X.  These timeouts delay boot of the AM654x by about 45 seconds.
> > > 
> > >   Move the BAR 0 initialization to ks_pcie_msi_host_init(), which is
> > >   only used for v3.65a devices, and remove ks_pcie_v3_65_add_bus().
> > 
> > I haven't heard anything so I amended it to the above.  But please
> > correct me if it's wrong.
> 
> I would suggest specifying the failing combination since I do not know
> if there is another device that is using v4.90a but doesn't see this
> issue. What is certain is that this issue is seen with the v4.90a
> controller on AM654x platform. Despite the PCIe Controller version
> remaining the same across different platforms, it might be possible
> that not all features supported by the PCIe Controller are enabled on
> all platforms. For that reason, it appears to me that the subject could
> be:
> 
>   PCI: keystone: Don't enable BAR 0 for AM654x
> 
> which implicitly indicates the combination as well (v4.90a on AM654x).
> 
> The commit message's contents could be reduced to:
> 
>   After 6ab15b5e7057 ("PCI: dwc: keystone: Convert .scan_bus()
>   callback to use add_bus"), ks_pcie_v3_65_add_bus() enabled BAR 0 for
>   both v3.65a and v4.90a devices.  On the AM654x SoC, which uses
>   v4.90a, enabling BAR 0 causes Completion Timeouts when setting up
>   MSI-X.  These timeouts delay boot of the AM654x by about 45 seconds.
> 
>   Move the BAR 0 initialization to ks_pcie_msi_host_init(), which is
>   only used for v3.65a devices, and remove ks_pcie_v3_65_add_bus().
> 
> by dropping:
> 
>   The BAR 0 initialization done by ks_pcie_v3_65_add_bus() should
>   happen for v3.65a devices only.  On other devices, BAR 0 should be
>   left disabled, as it is by dw_pcie_setup_rc().
> 
> The reason behind dropping the above paragraph is that BAR 0 could
> probably be enabled on other controller versions as well, but not on the
> v4.90a controller on the AM654x SoC.

Thanks, that makes good sense, I changed the subject and dropped that
paragraph.

Bjorn