linux-kernel - Re: [PATCH v2] PCI: qcom-ep: Enable controller resources like PHY only after refclk is available

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Message-ID: <20240828205945.GA37767@bhelgaas>
Date: Wed, 28 Aug 2024 15:59:45 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: lpieralisi@...nel.org, kw@...ux.com, bhelgaas@...gle.com,
	robh@...nel.org, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Subject: Re: [PATCH v2] PCI: qcom-ep: Enable controller resources like PHY
 only after refclk is available

On Wed, Aug 28, 2024 at 07:31:08PM +0530, Manivannan Sadhasivam wrote:
> qcom_pcie_enable_resources() is called by qcom_pcie_ep_probe() and it
> enables the controller resources like clocks, regulator, PHY. On one of the
> new unreleased Qcom SoC, PHY enablement depends on the active refclk. And
> on all of the supported Qcom endpoint SoCs, refclk comes from the host
> (RC). So calling qcom_pcie_enable_resources() without refclk causes the
> whole SoC crash on the new SoC.
> 
> qcom_pcie_enable_resources() is already called by
> qcom_pcie_perst_deassert() when PERST# is deasserted, and refclk is
> available at that time.
> 
> Hence, remove the unnecessary call to qcom_pcie_enable_resources() from
> qcom_pcie_ep_probe() to prevent the crash.
> 
> Fixes: 869bc5253406 ("PCI: dwc: ep: Fix DBI access failure for drivers requiring refclk from host")
> Tested-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> ---
> 
> Changes in v2:
> 
> - Changed the patch description to mention the crash clearly as suggested by
>   Bjorn

Clearly mentioning the crash as rationale for the change is *part* of
what I was looking for.

The rest, just as important, is information about what sort of crash
this is, because I hope and suspect the crash is recoverable, and we
*should* recover from it because PERST# may occur at arbitrary times,
so trying to avoid it is never going to be reliable.

Bjorn