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([2a01:e34:ed2f:f020:f457:5fc1:5262:84c]) by smtp.googlemail.com with ESMTPSA id o10sm9397248wrw.79.2020.08.07.02.40.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 07 Aug 2020 02:40:04 -0700 (PDT) Subject: Re: [GIT PULL] RESEND: thermal for v5.9-rc1 To: Linus Torvalds Cc: Zhang Rui , Amit Kucheria , Andrzej Pietrasiewicz , Colin King , Shawn Guo , Lukasz Luba , Sumeet Pawnikar , Henry Yen , Thierry Reding , Linux Kernel Mailing List , Linux PM mailing list , Marian-Cristian Rotariu References: From: Daniel Lezcano Message-ID: Date: Fri, 7 Aug 2020 11:40:02 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Linus, On 07/08/2020 04:43, Linus Torvalds wrote: > On Thu, Aug 6, 2020 at 1:19 PM Daniel Lezcano wrote: >> >> >> - Add generic netlink support for userspace notifications: events, >> temperature >> and discovery commands (Daniel Lezcano) > > This is "default y". > > Why? > > The help text doesn't explain either. > > Please explain, or remove the default y. We don't add new features and > then try to force people to use them by enabling them by default. > > "default y" is mainly for when something unconditional gets split up > and becomes conditional (so now "default y" means that you don't break > peoples setups when they don't even know what it is). > > Alternatively, "default y" is for things that are make peoples lives > immeasurably better somehow, and it would be a crime to not enable it > because it's _so_ wonderful. Well, I won't argue the netlink notification is so that fantastic but it is a feature that was needed since a long time. A previous partial implementation was directly compiled-in and then removed [1] because there were no user as it is and we wanted to introduce a clean new notification framework based in our previous discussion at Linux Plumbers Conference [2] but that needed some cleanups of the thermal core code before. This netlink framework fulfills the needs of the thermal daemons for Intel, Android HAL and SoC vendors which are hacking the thermal framework or constantly polling the temperature. Because the compilation failed if CONFIG_NET=n, the Kconfig option was introduced afterwards [3]. It could have been directly handled in the code with a 'ifdef' directive without option but it sounded more convenient to at least give the opportunity to opt-out the notification. It defaults to 'y' because the previous (but unused) implementation was unconditionally compiled-in and because of the thermal users needs. Is default=y wrong given this history? -- Daniel [1] https://patchwork.kernel.org/patch/11202093/ [2] https://www.linuxplumbersconf.org/event/2/contributions/185/attachments/39/46/LPC_2018_Thermal-Srinivas-Rui.pdf [3] https://git.kernel.org/pub/scm/linux/kernel/git/thermal/linux.git/commit/?h=thermal/next&id=5b8583d3bd7fc10cea07e4a5bfa59465758a39dc > So far, I'm not convinced we've ever hit that second case. > > Convince me that the thermal layer is so magical that it really > warrants it. Tell me why and how my life is improved by enabling it. > > Linus > -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog