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[94.29.21.60]) by smtp.googlemail.com with ESMTPSA id m18sm1039554ljg.105.2021.06.12.03.40.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 12 Jun 2021 03:40:30 -0700 (PDT) Subject: Re: [PATCH v1 03/10] ARM: tegra: acer-a500: Bump thermal trips by 10C To: Daniel Lezcano , =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= Cc: Thierry Reding , Jonathan Hunter , Agneli , Paul Fertser , Svyatoslav Ryhel , linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org References: <20210510202600.12156-1-digetx@gmail.com> <20210510202600.12156-4-digetx@gmail.com> <20210514211601.GA1969@qmqm.qmqm.pl> From: Dmitry Osipenko Message-ID: Date: Sat, 12 Jun 2021 13:40:30 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 11.06.2021 12:52, Daniel Lezcano пишет: > On 14/05/2021 23:16, Michał Mirosław wrote: >> On Mon, May 10, 2021 at 11:25:53PM +0300, Dmitry Osipenko wrote: >>> It's possible to hit the temperature of the thermal zone in a very warm >>> environment under a constant load, like watching a video using software >>> decoding. It's even easier to hit the limit with a slightly overclocked >>> CPU. Bump the temperature limit by 10C in order to improve user >>> experience. Acer A500 has a large board and 10" display panel which are >>> used for the heat dissipation, the SoC is placed far away from battery, >>> hence we can safely bump the temperature limit. >> >> 60^C looks like a touch-safety limit (to avoid burns for users). Did you >> verify the touchable parts' temperature somehow after the change? > > The skin temperature and the CPU/GPU etc ... temperatures are different > things. > > For the embedded system there is the dissipation system and a > temperature sensor on it which is the skin temp. This temperature is the > result of the heat of all the thermal zones on the board and must be > below 45°C. The temperature slowly changes. > > On the CPU, the temperature changes can be very fast and you have to > take care of keeping it below the max temperature specified in the TRM > by using different techniques (freq changes, idle injection, ...) but > the temperature can be 75°C, 85°C or whatever the manual says. > > 50°C and 60°C are low temperature for a CPU and that will inevitably > impact the performances, so setting the temperature close the max > temperature is what will allow max performances. > > What matters is the skin temperature. > > The skin temperature must be monitored by other techniques, eg. using > the TDP of the system and throttle the different devices to keep them in > this power budget. That is the role of an thermal daemon. Thank you for the clarification. Indeed, I wasn't sure how to make use of the skin temperature properly. The skin temperature varies a lot depending on the thermal capabilities of a particular device. It's about 15C below CPU core at a full load on A500, while it's 2C below CPU core on Nexus 7. But this is expected since Nexus 7 can't dissipate heat efficiently. I will revisit the DT thermal zones again for the next kernel release.