linux-kernel - Re: [PATCH v9 04/10] PCI: dwc: ep: Fix DBI access failure for drivers requiring refclk from host

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Date: Thu, 7 Mar 2024 21:31:12 +0100
From: Niklas Cassel <cassel@...nel.org>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: Jingoo Han <jingoohan1@...il.com>,
	Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Marek Vasut <marek.vasut+renesas@...il.com>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	Thierry Reding <thierry.reding@...il.com>,
	Jonathan Hunter <jonathanh@...dia.com>,
	Kishon Vijay Abraham I <kishon@...com>,
	Vidya Sagar <vidyas@...dia.com>,
	Vignesh Raghavendra <vigneshr@...com>,
	Richard Zhu <hongxing.zhu@....com>,
	Lucas Stach <l.stach@...gutronix.de>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	NXP Linux Team <linux-imx@....com>,
	Minghuan Lian <minghuan.Lian@....com>,
	Mingkai Hu <mingkai.hu@....com>, Roy Zang <roy.zang@....com>,
	Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Kishon Vijay Abraham I <kishon@...nel.org>,
	Jesper Nilsson <jesper.nilsson@...s.com>,
	Srikanth Thokala <srikanth.thokala@...el.com>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-renesas-soc@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	linux-tegra@...r.kernel.org, linux-omap@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
	linux-arm-kernel@...s.com, Frank Li <Frank.Li@....com>
Subject: Re: [PATCH v9 04/10] PCI: dwc: ep: Fix DBI access failure for
 drivers requiring refclk from host

On Mon, Mar 04, 2024 at 02:52:16PM +0530, Manivannan Sadhasivam wrote:
> The DWC glue drivers requiring an active reference clock from the PCIe host
> for initializing their PCIe EP core, set a flag called 'core_init_notifier'
> to let DWC driver know that these drivers need a special attention during
> initialization. In these drivers, access to the hw registers (like DBI)
> before receiving the active refclk from host will result in access failure
> and also could cause a whole system hang.
> 
> But the current DWC EP driver doesn't honor the requirements of the drivers
> setting 'core_init_notifier' flag and tries to access the DBI registers
> during dw_pcie_ep_init(). This causes the system hang for glue drivers such
> as Tegra194 and Qcom EP as they depend on refclk from host and have set the
> above mentioned flag.
> 
> To workaround this issue, users of the affected platforms have to maintain
> the dependency with the PCIe host by booting the PCIe EP after host boot.
> But this won't provide a good user experience, since PCIe EP is _one_ of
> the features of those platforms and it doesn't make sense to delay the
> whole platform booting due to PCIe requiring active refclk.
> 
> So to fix this issue, let's move all the DBI access from
> dw_pcie_ep_init() in the DWC EP driver to the dw_pcie_ep_init_complete()
> API. This API will only be called by the drivers setting
> 'core_init_notifier' flag once refclk is received from host. For the rest
> of the drivers that gets the refclk locally, this API will be called
> within dw_pcie_ep_init().
> 
> Fixes: e966f7390da9 ("PCI: dwc: Refactor core initialization code for EP mode")
> Co-developed-by: Vidya Sagar <vidyas@...dia.com>
> Signed-off-by: Vidya Sagar <vidyas@...dia.com>
> Reviewed-by: Frank Li <Frank.Li@....com>
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> ---

I'm not sure if the Fixes tag is stictly correct, since there is
nothing wrong with the commit that the Fixes-tag is referencing.

What this patch addresses is an additional use-case/feature,
which allows you to start the EP-side before the RC-side.

However, I'm guessing that you kept the Fixes-tag such that this
patch will get backported. However, this patch is number 4/10 in
the patch series. If this is a strict fix that you want backported,
and it does not depend on any of the previous patches (it doesn't
seem that way), then I think that you should have put it as patch
1/10 in the series.

Patch ordering aside:
Reviewed-by: Niklas Cassel <cassel@...nel.org>