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(p200300ea8f0655007409b9665a79f8df.dip0.t-ipconnect.de. [2003:ea:8f06:5500:7409:b966:5a79:f8df]) by smtp.googlemail.com with ESMTPSA id c10sm97895791wrb.92.2021.01.04.12.32.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 04 Jan 2021 12:32:54 -0800 (PST) Subject: Re: Time to re-enable Runtime PM per default for PCI devcies? To: Lukas Wunner Cc: "Rafael J. Wysocki" , Bjorn Helgaas , "Rafael J. Wysocki" , Bjorn Helgaas , Mika Westerberg , Kai Heng Feng , "linux-pci@vger.kernel.org" , Linux PM , Linux Kernel Mailing List References: <79940973-b631-90f9-dbc4-9579c6000816@gmail.com> <20201117163817.GA1397220@bjorn-Precision-5520> <9ca0fb46-9e65-31e2-103f-1c98ce8362c7@gmail.com> <20201231040735.GA2075@wunner.de> <4eb10092-e3f9-c9be-2dec-e6de8aeedf97@gmail.com> <20210104173944.GA31187@wunner.de> From: Heiner Kallweit Message-ID: Date: Mon, 4 Jan 2021 21:32:48 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <20210104173944.GA31187@wunner.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04.01.2021 18:39, Lukas Wunner wrote: > On Thu, Dec 31, 2020 at 10:38:12AM +0100, Heiner Kallweit wrote: >> On 31.12.2020 05:07, Lukas Wunner wrote: >>> FWIW, if platform_pci_power_manageable() returns true, it can probably >>> be assumed that allowing runtime PM by default is okay. So as a first >>> step, you may want to call that instead of adding a new callback. >> >> I don't think that's sufficient. Most likely all the broken old systems >> return true for platform_pci_power_manageable(). > > platform_pci_power_manageable() is not a global flag, but rather > a per-device flag whether the platform is capable of power-managing > that device. E.g. for the ACPI platform, it indicates that objects > such as _PS0 or _PS3 are present in the device's namespace. > > My point is that if the platform can power-manage a device, > then it ought to be safe to enable runtime PM by default for it. > Not sure about that. Just that the BIOS claims it can power-manage the device, doesn't rule out that it's broken and fails to do so. > If you insist on a "big hammer" approach by turning on runtime PM > by default for everything, you risk regressions. You can avoid > that by going for a smart approach which enables runtime PM in > cases when it's safe. > > Thanks, > > Lukas > Heiner