From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 04CAF219F8 for ; Fri, 13 Oct 2023 16:42:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="b86OTm7/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1C518C433C8; Fri, 13 Oct 2023 16:42:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1697215350; bh=MqC3yrRRj3UMGOPti8ERknVNqGEUu0oFiV03E0Vidv0=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=b86OTm7/vWPz1lXdWBiZn7RcGveX1aFsvL5jmXTq2YbcyNGIbGhWA6q1/AnMGbd1N IFYYegR+vc8lMskeUk8lajThoc+bo1PlPWPhNqD2fwOG3AfKYpg90Eza/kNH0uSNPW Jky7Vj9783vlIkTQS3O7jJucPYVzjXAq/DJZUjUVY+A/BEROWzFLMN0GpWgbN/I8Vu ImQsRWZuesvRBHjxd0H3/8ZdxSWJjJnhbYb4F5CAQ1P15D5R2lTSA+hkWwJq0LpHAe Bn/6fD9G+fr9mHm/5sCM1EEe3TdFQCGEcv6U3ysqKGhpLI6CBcvRuzJ9zOUE+g+0U1 YdquVEXDnza8g== Date: Fri, 13 Oct 2023 11:42:28 -0500 From: Bjorn Helgaas To: Ilpo =?utf-8?B?SsOkcnZpbmVu?= Cc: "Rafael J . Wysocki" , linux-pci@vger.kernel.org, Lorenzo Pieralisi , Rob Herring , Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= , Lukas Wunner , Heiner Kallweit , Emmanuel Grumbach , LKML , Bjorn Helgaas , ath10k@lists.infradead.org, ath11k@lists.infradead.org, ath12k@lists.infradead.org, intel-wired-lan@lists.osuosl.org, linux-arm-kernel@lists.infradead.org, linux-bluetooth@vger.kernel.org, linux-mediatek@lists.infradead.org, linux-rdma@vger.kernel.org, linux-wireless@vger.kernel.org, Netdev Subject: Re: [PATCH v2 03/13] PCI/ASPM: Disable ASPM when driver requests it Message-ID: <20231013164228.GA1117889@bhelgaas> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Thu, Oct 12, 2023 at 01:56:16PM +0300, Ilpo Järvinen wrote: > On Wed, 11 Oct 2023, Bjorn Helgaas wrote: > > On Mon, Sep 18, 2023 at 04:10:53PM +0300, Ilpo Järvinen wrote: > > > PCI core/ASPM service driver allows controlling ASPM state through > > > pci_disable_link_state() and pci_enable_link_state() API. It was > > > decided earlier (see the Link below), to not allow ASPM changes when OS > > > does not have control over it but only log a warning about the problem > > > (commit 2add0ec14c25 ("PCI/ASPM: Warn when driver asks to disable ASPM, > > > but we can't do it")). Similarly, if ASPM is not enabled through > > > config, ASPM cannot be disabled. > ... > > This disables *all* ASPM states, unlike the version when > > CONFIG_PCIEASPM is enabled. I suppose there's a reason, and maybe a > > comment could elaborate on it? > > > > When CONFIG_PCIEASPM is not enabled, I don't think we actively > > *disable* ASPM in the hardware; we just leave it as-is, so firmware > > might have left it enabled. > > This whole trickery is intended for drivers that do not want to have ASPM > because the devices are broken with it. So leaving it as-is is not really > an option (as demonstrated by the custom workarounds). Right. > > Conceptually it seems like the LNKCTL updates here should be the same > > whether CONFIG_PCIEASPM is enabled or not (subject to the question > > above). > > > > When CONFIG_PCIEASPM is enabled, we might need to do more stuff, but > > it seems like the core should be the same. > > So you think it's safer to partially disable ASPM (as per driver's > request) rather than disable it completely? I got the impression that the > latter might be safer from what Rafael said earlier but I suppose I might > have misinterpreted him since he didn't exactly say that it might be safer > to _completely_ disable it. My question is whether the state of the device should depend on CONFIG_PCIEASPM. If the driver does this: pci_disable_link_state(PCIE_LINK_STATE_L0S) do we want to leave L1 enabled when CONFIG_PCIEASPM=y but disable L1 when CONFIG_PCIEASPM is unset? I can see arguments both ways. My thought was that it would be nice to end up with a single implementation of pci_disable_link_state() with an #ifdef around the CONFIG_PCIEASPM-enabled stuff because it makes the code easier to read. Bjorn