Re: [PATCH v7 0/2] PCI: designware-ep: Fix DBI access before core init

From: Niklas Cassel <Niklas.Cassel@wdc.com>
To: "Krzysztof Wilczyński" <kw@linux.com>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>,
	"jingoohan1@gmail.com" <jingoohan1@gmail.com>,
	"gustavo.pimentel@synopsys.com" <gustavo.pimentel@synopsys.com>,
	"lpieralisi@kernel.org" <lpieralisi@kernel.org>,
	"robh@kernel.org" <robh@kernel.org>,
	"bhelgaas@google.com" <bhelgaas@google.com>,
	"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
	"linux-arm-msm@vger.kernel.org" <linux-arm-msm@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"quic_bjorande@quicinc.com" <quic_bjorande@quicinc.com>,
	"fancer.lancer@gmail.com" <fancer.lancer@gmail.com>,
	"vidyas@nvidia.com" <vidyas@nvidia.com>
Subject: Re: [PATCH v7 0/2] PCI: designware-ep: Fix DBI access before core init
Date: Tue, 9 Jan 2024 17:58:53 +0000	[thread overview]
Message-ID: <ZZ2JXMhdOI1Upabx@x1-carbon> (raw)
In-Reply-To: <20240107072707.GC3450972@rocinante>

On Sun, Jan 07, 2024 at 04:27:07PM +0900, Krzysztof Wilczyński wrote:
> Hello,

Hello Krzysztof, Manivannan,

> 
> > This series is the continuation of previous work by Vidya Sagar [1] to fix the
> > issues related to accessing DBI register space before completing the core
> > initialization in some EP platforms like Tegra194/234 and Qcom SM8450.
> 
> Applied to controller/dwc-ep, thank you!
> 
> [01/02] PCI: designware-ep: Fix DBI access before core init
>         https://git.kernel.org/pci/pci/c/d3d13b00a2cf
> [02/02] PCI: designware-ep: Move pci_epc_init_notify() inside dw_pcie_ep_init_complete()
>         https://git.kernel.org/pci/pci/c/a171e1d60dad
> 
> 	Krzysztof

Considering that we know that this series introduces new problems
for drivers with a .core_init_notifier (i.e. tegra and qcom), see:
https://lore.kernel.org/linux-pci/ZWYmX8Y%2F7Q9WMxES@x1-carbon/

Do we really want to apply this series as is?

Reading the patch, it appears that (at least some) tegra and
qcom boards currently causes a whole system hang, which IIUC,
renders those boards unusable.

So perhaps the new issues introduced by this series is preferable
to a whole system hang.

As such, I can understand the urgency to merge this series.
However, at the very least, I think that it might be worth amending
the commit message to mention that this will currently not deregister
the dma device in a clean way, leading to e.g. superfluous entries in
/sys/class/dma/ and debugfs warnings being printed to dmesg.

Kind regards,
Niklas