linux-kernel - Re: [PATCH V4 0/3] PCI: designware-ep: Fix DBI access before core init

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Date:   Mon, 19 Sep 2022 17:40:14 -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, mani@...nel.org,
        Sergey.Semin@...kalelectronics.ru, dmitry.baryshkov@...aro.org,
        linmq006@...il.com, ffclaire1224@...il.com,
        thierry.reding@...il.com, jonathanh@...dia.com,
        linux-pci@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, kthota@...dia.com,
        mmaddireddy@...dia.com, sagar.tv@...il.com
Subject: Re: [PATCH V4 0/3] PCI: designware-ep: Fix DBI access before core
 init

On Tue, Sep 20, 2022 at 12:03:39AM +0530, Vidya Sagar wrote:
> This series attempts to fix the issue with core register (Ex:- DBI) accesses
> causing system hang issues in platforms where there is a dependency on the
> availability of PCIe Reference clock from the host for their core
> initialization.
> This series is verified on Tegra194 & Tegra234 platforms.

I think this design is just kind of weird, specifically, the fact that
setting .core_init_notifier makes dw_pcie_ep_init() bail out early.
The usual pattern is more like "if the specific driver sets this
function pointer, the generic code calls it."

The name "dw_pcie_ep_init_complete()" is not as helpful as it could
be: it tells us something about what has happened before this point,
but it doesn't tell us anything about what dw_pcie_ep_init_complete()
*does*.

Same thing with dw_pcie_ep_init_notify() -- it doesn't tell us
anything about what the function *does*.  I see that it calls
pci_epc_init_notify(), which calls a notifier call chain (currently
always empty except for a test case).  I think pci_epc_linkup() is a
better name because it says something about what's happening: the link
is now up and we're telling somebody about it.  "pci_epc_init_notify()"
doesn't convey that.  "pci_epc_core_initialized()" might.

It looks like both qcom and tegra wait for an interrupt before calling
dw_pcie_ep_init_notify(), but I'm a little concerned because I can't
figure out what specifically they do to start the process that
ultimately generates the interrupt.  Presumably they request the IRQ
*before* starting the process, but there's not much between the
devm_request_threaded_irq() and the interrupt handler, which makes me
wonder if both are racy.

> Manivannan, could you please verify on qcom platforms?
> 
> V4:
> * Addressed review comments from Bjorn and Manivannan
> * Added .ep_init_late() ops
> * Added patches to refactor code in qcom and tegra platforms
> 
> Vidya Sagar (3):
>   PCI: designware-ep: Fix DBI access before core init
>   PCI: qcom-ep: Refactor EP initialization completion
>   PCI: tegra194: Refactor EP initialization completion
> 
>  .../pci/controller/dwc/pcie-designware-ep.c   | 112 ++++++++++--------
>  drivers/pci/controller/dwc/pcie-designware.h  |  10 +-
>  drivers/pci/controller/dwc/pcie-qcom-ep.c     |  27 +++--
>  drivers/pci/controller/dwc/pcie-tegra194.c    |   4 +-
>  4 files changed, 85 insertions(+), 68 deletions(-)
> 
> -- 
> 2.17.1
>