linux-kernel - Re: [PATCH v9 07/10] PCI: dwc: ep: Remove "core_init

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Date: Mon, 11 Mar 2024 20:15:59 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Niklas Cassel <cassel@...nel.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 07/10] PCI: dwc: ep: Remove "core_init_notifier" flag

On Fri, Mar 08, 2024 at 02:24:35PM +0100, Niklas Cassel wrote:
> On Mon, Mar 04, 2024 at 02:52:19PM +0530, Manivannan Sadhasivam wrote:
> > "core_init_notifier" flag is set by the glue drivers requiring refclk from
> > the host to complete the DWC core initialization. Also, those drivers will
> > send a notification to the EPF drivers once the initialization is fully
> > completed using the pci_epc_init_notify() API. Only then, the EPF drivers
> > will start functioning.
> > 
> > For the rest of the drivers generating refclk locally, EPF drivers will
> > start functioning post binding with them. EPF drivers rely on the
> > 'core_init_notifier' flag to differentiate between the drivers.
> > Unfortunately, this creates two different flows for the EPF drivers.
> > 
> > So to avoid that, let's get rid of the "core_init_notifier" flag and follow
> > a single initialization flow for the EPF drivers. This is done by calling
> > the dw_pcie_ep_init_notify() from all glue drivers after the completion of
> > dw_pcie_ep_init_registers() API. This will allow all the glue drivers to
> > send the notification to the EPF drivers once the initialization is fully
> > completed.
> > 
> > Only difference here is that, the drivers requiring refclk from host will
> > send the notification once refclk is received, while others will send it
> > during probe time itself.
> > 
> > Reviewed-by: Frank Li <Frank.Li@....com>
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > ---
> > diff --git a/drivers/pci/endpoint/functions/pci-epf-test.c b/drivers/pci/endpoint/functions/pci-epf-test.c
> > index 18c80002d3bd..fc0282b0d626 100644
> > --- a/drivers/pci/endpoint/functions/pci-epf-test.c
> > +++ b/drivers/pci/endpoint/functions/pci-epf-test.c
> > @@ -927,21 +928,12 @@ static int pci_epf_test_bind(struct pci_epf *epf)
> >  	if (ret)
> >  		return ret;
> >
> 
> Hello Mani,
> 
> Since you asked for testing, I gave your series a spin
> (with a driver without .core_init_notifier).
> 
> 
> There seems to be a problem that pci_epc_write_header() is never called.
> 
> Debugging this, it seems that .core_init in pci-epf-test is never called.
> 
> If I add debug prints in pci_epc_init_notify(), I see that it does not
> notify a single EPF driver.
> 
> It appears that the patch in $subject will call pci_epc_init_notify()
> at EPC driver .probe() time, and at that point in time, there are no
> EPF drivers registered.
> 
> They get registered later, when doing the configfs write.
> 
> 
> I would say that it is the following change that breaks things:
> 
> > -	if (!core_init_notifier) {
> > -		ret = pci_epf_test_core_init(epf);
> > -		if (ret)
> > -			return ret;
> > -	}
> > -
> 
> Since without this code, pci_epf_test_core_init() will no longer be called,
> as there is currently no one that calls epf->core_init() for a EPF driver
> after it has been bound. (For drivers that call dw_pcie_ep_init_notify() in
> .probe())
> 

Thanks a lot for testing, Niklas!

> I guess one way to solve this would be for the EPC core to keep track of
> the current EPC "core state" (up/down). If the core is "up" at EPF .bind()
> time, notify the EPF driver directly after .bind()?
> 

Yeah, that's a good solution. But I think it would be better if the EPC caches
all events if the EPF drivers are not available and dispatch them once the bind
happens for each EPF driver. Even though INIT_COMPLETE is the only event that is
getting generated before bind() now, IMO it is better to add provision to catch
other events also.

Wdyt?

- Mani

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