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

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Message-ID: <20240313175333.GA126027@thinkpad>
Date: Wed, 13 Mar 2024 23:23:33 +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 Mon, Mar 11, 2024 at 10:54:28PM +0100, Niklas Cassel wrote:
> On Mon, Mar 11, 2024 at 08:15:59PM +0530, Manivannan Sadhasivam wrote:
> > > 
> > > 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?
> 
> I'm not sure.
> What if the EPF goes up/down/up, it seems a bit silly to send all those
> events to the EPF driver that will alloc+free+alloc.
> 
> Do we know for sure that we will want to store + replay events other than
> INIT_COMPLETE?
> 
> And how many events should we store?
> 
> 
> Until we can think of a good reason which events other than UP/DOWN we
> can to store, I think that just storing the state as an integer in
> struct pci_epc seems simpler.
> 

Hmm, makes sense.

> 
> Or I guess we could continue with a flag in struct pci_epc_features,
> like has_perst_notifier, which would then require the EPC driver to
> call both epc_notify_core_up() and epc_notify_core_down() when receiving
> the PERST deassert/assert.
> For a driver without the flag set, the EPC core would call
> .epc_notify_core_up() after bind. (And .epc_notify_core_down() would never
> be called, or it could call it before unbind().)
> That way an EPF driver itself would not need any different handling
> (all callbacks would always come, either triggered by an EPC driver that
> has PERST GPIO irq, or triggered by the EPC core for a driver that lacks
> a PERST GPIO).
> 

For simplicity, I've just used a flag in 'struct pci_epc' to track the core_init
and call the callback during bind().

But the series has grown big, so I decided to split it into two. One to address
the DBI access issue and also remove the 'core_init_notifier' flag and another
one to make EPF drivers more robust to handle the host reboot scenario.

- Mani

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