linux-kernel - Re: [PATCH] PCI: qcom-ep: Do not enable resources during probe()

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Message-ID: <20240816120214.GA65249@bhelgaas>
Date: Fri, 16 Aug 2024 07:02:14 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: lpieralisi@...nel.org, kw@...ux.com, robh@...nel.org,
	bhelgaas@...gle.com, linux-arm-msm@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: qcom-ep: Do not enable resources during probe()

On Fri, Aug 16, 2024 at 11:07:57AM +0530, Manivannan Sadhasivam wrote:
> On Thu, Aug 15, 2024 at 01:15:57PM -0500, Bjorn Helgaas wrote:
> > On Sat, Jul 27, 2024 at 02:36:04PM +0530, Manivannan Sadhasivam wrote:
> > > Starting from commit 869bc5253406 ("PCI: dwc: ep: Fix DBI access failure
> > > for drivers requiring refclk from host"), all the hardware register access
> > > (like DBI) were moved to dw_pcie_ep_init_registers() which gets called only
> > > in qcom_pcie_perst_deassert() i.e., only after the endpoint received refclk
> > > from host.
> > > 
> > > So there is no need to enable the endpoint resources (like clk, regulators,
> > > PHY) during probe(). Hence, remove the call to qcom_pcie_enable_resources()
> > > helper from probe(). This was added earlier because dw_pcie_ep_init() was
> > > doing DBI access, which is not done now.
> > > 
> > > While at it, let's also call dw_pcie_ep_deinit() in err path to deinit the
> > > EP controller in the case of failure.
> > 
> > Is this v6.11 material?  If so, we need a little more justification
> > than "no need to enable".
> 
> That's why I asked to merge the comment from Dmitry:
> 
> "...moreover his makes PCIe EP fail on some of the platforms as powering on PHY
> requires refclk from the RC side, which is not enabled at the probe time."

The patch was posted and described basically as a cleanup of something
that was unnecessary but not harmful, which is not post-merge window
material.

If it is in fact a critical fix, that needs to be the central point of
the commit log, not something tacked on with "moreover" or
"additionally".  And we need something like a Fixes: tag so we know
when the problem was introduced and where to backport this.

Bjorn