From: Jon Hunter <jonathanh@nvidia.com>
To: Bjorn Helgaas <helgaas@kernel.org>, Vidya Sagar <vidyas@nvidia.com>
Cc: <lorenzo.pieralisi@arm.com>, <bhelgaas@google.com>,
<robh+dt@kernel.org>, <amurray@thegoodpenguin.co.uk>,
<gustavo.pimentel@synopsys.com>, <jingoohan1@gmail.com>,
<Joao.Pinto@synopsys.com>, Thierry Reding <treding@nvidia.com>,
Krishna Thota <kthota@nvidia.com>, <linux-pci@vger.kernel.org>,
<linux-kernel@vger.kernel.org>
Subject: Re: Query regarding the use of pcie-designware-plat.c file
Date: Wed, 9 Jun 2021 17:54:38 +0100 [thread overview]
Message-ID: <2970bdf2-bef2-bdcb-6ee3-ac1181d97b78@nvidia.com> (raw)
In-Reply-To: <20210609163010.GA2643779@bjorn-Precision-5520>
On 09/06/2021 17:30, Bjorn Helgaas wrote:
> On Wed, Jun 09, 2021 at 12:52:37AM +0530, Vidya Sagar wrote:
>> Hi,
>> I would like to know what is the use of pcie-designware-plat.c file. This
>> looks like a skeleton file and can't really work with any specific hardware
>> as such.
>> Some context for this mail thread is, if the config CONFIG_PCIE_DW_PLAT is
>> enabled in a system where a Synopsys DesignWare IP based PCIe controller is
>> present and its configuration is enabled (Ex:- Tegra194 system with
>> CONFIG_PCIE_TEGRA194_HOST enabled), then, it can so happen that the probe of
>> pcie-designware-plat.c called first (because all DWC based PCIe controller
>> nodes have "snps,dw-pcie" compatibility string) and can crash the system.
>
> What's the crash? If a device claims to be compatible with
> "snps,dw-pcie" and pcie-designware-plat.c claims to know how to
> operate "snps,dw-pcie" devices, it seems like something is wrong.
>
> "snps,dw-pcie" is a generic device type, so pcie-designware-plat.c
> might not know how to operate device-specific details of some of those
> devices, but basic functionality should work and it certainly
> shouldn't crash.
It is not really a crash but a hang when trying to access the hardware
before it has been properly initialised.
The scenario I saw was that if the Tegra194 PCIe driver was built as a
module but the pcie-designware-plat.c was built into the kernel, then on
boot we would attempt to probe the pcie-designware-plat.c driver because
module was not available yet and this would hang. Hence, I removed the
"snps,dw-pcie" compatible string for Tegra194 to avoid this and ONLY
probe the Tegra194 PCIe driver.
Sagar is wondering why this hang is only seen/reported for Tegra and
could this happen to other platforms? I think that is potentially could.
Jon
--
nvpublic
next prev parent reply other threads:[~2021-06-09 16:54 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-08 19:22 Query regarding the use of pcie-designware-plat.c file Vidya Sagar
2021-06-08 21:17 ` Gustavo Pimentel
2021-06-09 5:26 ` Vidya Sagar
2021-06-09 9:49 ` Thierry Reding
2021-06-15 3:28 ` Vidya Sagar
2021-06-09 16:30 ` Bjorn Helgaas
2021-06-09 16:54 ` Jon Hunter [this message]
2021-06-15 19:42 ` Bjorn Helgaas
2021-06-15 21:05 ` Rob Herring
2021-06-16 7:54 ` Jon Hunter
2021-06-20 13:35 ` Vidya Sagar
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