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Message-ID: <20220728141716.GA296915@bhelgaas>
Date: Thu, 28 Jul 2022 09:17:16 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Vidya Sagar <vidyas@...dia.com>
Cc: jingoohan1@...il.com, gustavo.pimentel@...opsys.com,
lpieralisi@...nel.org, robh@...nel.org, kw@...ux.com,
bhelgaas@...gle.com, linux-pci@...r.kernel.org,
linux-kernel@...r.kernel.org, kthota@...dia.com,
mmaddireddy@...dia.com, sagar.tv@...il.com
Subject: Re: [PATCH V1] PCI: designware-ep: Fix DBI access before core init
On Thu, Jul 28, 2022 at 05:56:28PM +0530, Vidya Sagar wrote:
>
>
> On 7/28/2022 3:44 AM, Bjorn Helgaas wrote:
> > External email: Use caution opening links or attachments
> >
> >
> > On Wed, Jun 22, 2022 at 09:31:33AM +0530, Vidya Sagar wrote:
> > > Platforms that cannot support their core initialization without the
> > > reference clock from the host, implement the feature 'core_init_notifier'
> > > to indicate the DesignWare sub-system about when their core is getting
> > > initialized. Any accesses to the core (Ex:- DBI) would result in system
> > > hang in such systems (Ex:- tegra194). This patch moves any access to the
> > > core to dw_pcie_ep_init_complete() API which is effectively called only
> > > after the core initialization.
> >
> > I assume this is still broken. I want to fix it. I assume this patch
> > fixes it and there are no known problems with it. I assume this can
> > be fixed so it works on all platforms, whether they use
> > core_init_notifier or not.
> Yes. All your assumptions are correct.
>
> >
> > I'd like the commit log to be specific about where the hang occurs so
> > it's easy for a non-DesignWare expert (me!) to see the problem. E.g.,
> > on tegra194, X depends on Y, but Y is initialized after X. Say
> > specifically what functions X and Y are.
> X = DBI accesses
> Y = Core initialization which in turn depends on the REFCLK from the host
>
> Without this patch, hang happens when DBI registers are accessed without
> core being initialized. In the case of Tegra194 at least, core gets
> initialized only after REFCLK is available from the host. The way we make
> sure that the REFCLK is available from the host is by checking for PERST#
> de-assertion interrupt. (PCIe spec mandates that the host must supply REFCLK
> before de-asserting PERST# signal).
> This patch prevents any accesses to the DBI/Core registers if the platform
> says that it supports core_init_notifier.
That's basically what the commit log already said. Can you give me
actual function names as a hint for where to look?
Bjorn
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