Re: [PATCH v2 1/4] PCI: dwc: Advertise L1 PM Substates only if driver requests it

From: Bjorn Helgaas <helgaas@kernel.org>
To: Manivannan Sadhasivam <mani@kernel.org>
Cc: "Niklas Cassel" <cassel@kernel.org>,
	"Shawn Lin" <shawn.lin@rock-chips.com>,
	"Lorenzo Pieralisi" <lpieralisi@kernel.org>,
	"Krzysztof Wilczyński" <kwilczynski@kernel.org>,
	"Rob Herring" <robh@kernel.org>,
	"Heiko Stuebner" <heiko@sntech.de>,
	"Kever Yang" <kever.yang@rock-chips.com>,
	"Simon Xue" <xxm@rock-chips.com>,
	"Damien Le Moal" <dlemoal@kernel.org>,
	"Dragan Simic" <dsimic@manjaro.org>,
	"FUKAUMI Naoki" <naoki@radxa.com>,
	"Diederik de Haas" <diederik@cknow-tech.com>,
	"Richard Zhu" <hongxing.zhu@nxp.com>,
	"Frank Li" <Frank.li@nxp.com>,
	"Lucas Stach" <l.stach@pengutronix.de>,
	"Shawn Guo" <shawnguo@kernel.org>,
	"Sascha Hauer" <s.hauer@pengutronix.de>,
	"Fabio Estevam" <festevam@gmail.com>,
	"Conor Dooley" <conor@kernel.org>,
	"Krzysztof Kozlowski" <krzk@kernel.org>,
	"Thierry Reding" <thierry.reding@gmail.com>,
	"Jonathan Hunter" <jonathanh@nvidia.com>,
	"Hans Zhang" <hans.zhang@cixtech.com>,
	linux-tegra@vger.kernel.org, linux-pci@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-rockchip@lists.infradead.org, kernel@pengutronix.de,
	"Bjorn Helgaas" <bhelgaas@google.com>
Subject: Re: [PATCH v2 1/4] PCI: dwc: Advertise L1 PM Substates only if driver requests it
Date: Mon, 24 Nov 2025 15:19:03 -0600	[thread overview]
Message-ID: <20251124211903.GA2712341@bhelgaas> (raw)
In-Reply-To: <wja7vxtg7bqq2udepl5r3mvgg5swvuqtuzk6cnimgcbw2aegqs@hru6yzg4xx3o>

On Thu, Nov 20, 2025 at 01:10:56PM +0530, Manivannan Sadhasivam wrote:
> On Tue, Nov 18, 2025 at 03:42:15PM -0600, Bjorn Helgaas wrote:
> > From: Bjorn Helgaas <bhelgaas@google.com>
> > 
> > L1 PM Substates require the CLKREQ# signal and may also require
> > device-specific support.  If CLKREQ# is not supported or driver support is
> > lacking, enabling L1.1 or L1.2 may cause errors when accessing devices,
> > e.g.,
> > 
> >   nvme nvme0: controller is down; will reset: CSTS=0xffffffff, PCI_STATUS=0x10
> > 
> > If the kernel is built with CONFIG_PCIEASPM_POWER_SUPERSAVE=y or users
> > enable L1.x via sysfs, users may trip over these errors even if L1
> > Substates haven't been enabled by firmware or the driver.
> > 
> > To prevent such errors, disable advertising the L1 PM Substates unless the
> > driver sets "dw_pcie.l1ss_support" to indicate that it knows CLKREQ# is
> > present and any device-specific configuration has been done.
> 
> Going by this reasoning, why can't we enable L1 PM Substates for
> these platforms by default?

I think we can, in a separate series.  I don't have time to deal with
this before the v6.19 merge window, but you can certainly do that.

Bjorn