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[95.49.139.62]) by smtp.gmail.com with ESMTPSA id w3sm8852696wrn.31.2020.03.21.12.26.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 21 Mar 2020 12:26:24 -0700 (PDT) Subject: Re: HW LED triggers again To: Marek Behun Cc: linux-leds@vger.kernel.org, Pavel Machek References: <20200320204308.411f8d68@nic.cz> From: Jacek Anaszewski Autocrypt: addr=jacek.anaszewski@gmail.com; prefer-encrypt=mutual; keydata= xsFNBFWjfaEBEADd66EQbd6yd8YjG0kbEDT2QIkx8C7BqMXR8AdmA1OMApbfSvEZFT1D/ECR eWFBS8XtApKQx1xAs1j5z70k3zebk2eeNs5ahxi6vM4Qh89vBM46biSKeeX5fLcv7asmGb/a FnHPAfQaKFyG/Bj9V+//ef67hpjJWR3s74C6LZCFLcbZM0z/wTH+baA5Jwcnqr4h/ygosvhP X3gkRzJLSFYekmEv+WHieeKXLrJdsUPUvPJTZtvi3ELUxHNOZwX2oRJStWpmL2QGMwPokRNQ 29GvnueQdQrIl2ylhul6TSrClMrKZqOajDFng7TLgvNfyVZE8WQwmrkTrdzBLfu3kScjE14Q Volq8OtQpTsw5570D4plVKh2ahlhrwXdneSot0STk9Dh1grEB/Jfw8dknvqkdjALUrrM45eF FM4FSMxIlNV8WxueHDss9vXRbCUxzGw37Ck9JWYo0EpcpcvwPf33yntYCbnt+RQRjv7vy3w5 osVwRR4hpbL/fWt1AnZ+RvbP4kYSptOCPQ+Pp1tCw16BOaPjtlqSTcrlD2fo2IbaB5D21SUa IsdZ/XkD+V2S9jCrN1yyK2iKgxtDoUkWiqlfRgH2Ep1tZtb4NLF/S0oCr7rNLO7WbqLZQh1q ShfZR16h7YW//1/NFwnyCVaG1CP/L/io719dPWgEd/sVSKT2TwARAQABzS1KYWNlayBBbmFz emV3c2tpIDxqYWNlay5hbmFzemV3c2tpQGdtYWlsLmNvbT7Cwa8EEwEIAEICGwMHCwkIBwMC AQYVCAIJCgsDFgIBAh4BAheAAhkBFiEEvx38ClaPBfeVdXCQvWpQHLeLfCYFAl5O5twFCRIR arsAIQkQvWpQHLeLfCYWIQS/HfwKVo8F95V1cJC9alAct4t8JhIgEACtWz3zR5uxaU/GozHh iZfiyUTomQpGNvAtjjZE6UKO/cKusCcvOv0FZbfGDajcMIU8f3FUxJdybrY86KJ9a3tOddal KtB2of3/Ot/EIQjpQb28iLoY8AWnf9G4LQZtoXHiUcOAVPkKgCFnz1IENK3uvyCB9c9//KhE cRZkeAIE2sTmcI4k7/dNHpRI4nha/ZytPwTdM3BjAfxxQI5nMLptm1ksEBI7W1SDOnY3dG2J QWmqpxIefjgyiy0aU+jAw1x3RdZrokVD8OCJiJM8+Z36imarEzqIRQLh+sDNLfV3wEaBn/HU 0Vj6VrRyW2K0jAYToRFD3Ay/eGSfOOAEr/LoMr3NBTDkRLEWdOozllOwADEY9wH0BLHMp2WI hXGOStNiroIEhW2/E0udFJo9b3VoOWKWl+zcUP/keLxVUCXhpmeS7VpSkqsrCVqTVkEc8AXq xhJXeIQJC/XRpCYFc3pFUlVCFViF1ZU2OzE8TndRzzD8e/9ETrJ1GAYa78tNopYhY6AbGlv4 U01nIC93bK07O4IhtBAKsiUz3JPX/KA/dXJOC86qP373cVWVYPvZW+KOya9/7rz0MGR1az9G HqJB7q7DVcCQKt9Egae/goznnXbET6ivCNKbqkH3n/JpiPIxkaXVrbn3QlVtzYpROsS/pCOp 5Evig7kql5L0aYJIZs4zBFsKioYWCSsGAQQB2kcPAQEHQFCKEG5pCgebryz66pTa9eAo+r8y TkMEEnG8UR5oWFt3wsIbBBgBCAAgFiEEvx38ClaPBfeVdXCQvWpQHLeLfCYFAlsKioYCGwIA rwkQvWpQHLeLfCaNIAQZFggAHRYhBBTDHErITmX+em3wBGIQbFEb9KXbBQJbCoqGACEJEGIQ bFEb9KXbFiEEFMMcSshOZf56bfAEYhBsURv0pdvELgD/U+y3/hsz0bIjMQJY0LLxM/rFY9Vz 1L43+lQHXjL3MPsA/1lNm5sailsY7aFBVJxAzTa8ZAGWBdVaGo6KCvimDB8GFiEEvx38ClaP BfeVdXCQvWpQHLeLfCbuOg/+PH6gY6Z1GiCzuYb/8f7D0NOcF8+md+R6KKiQZij/6G5Y7lXQ Bz21Opl4Vz/+39i5gmfBa9LRHH4ovR9Pd6H0FCjju4XjIOJkiJYs2HgCCm6nUxRJWzPgyMPS VbqCG2ctwaUiChUdbS+09bWb2MBNjIlI4b8wLWIOtxhyn25Vifm0p+QR5A2ym4bqJJ9LSre1 qM8qdPWcnExPFU4PZFYQgZ9pX1Jyui73ZUP94L7/wg1GyJZL3ePeE4ogBXldE0g0Wq3ORqA9 gA/yvrCSyNKOHTV9JMGnnPGN+wjBYMPMOuqDPC/zcK+stdFXc6UbUM1QNgDnaomvjuloflAx aYdblM26gFfypvpFb8czcPM+BP6X6vWk+Mw9+8vW3tyK9lSg+43OjIWlBGPpO9aLZsYYxAqv J5iSxcbbOLb5q8wWct6U7EZ1RnuOfVInoBttrlYvdWtcI/5NQTptkuB/DyRhrxBJc/fKzJ4w jS2ikcWe0FnxrQpcE2yqoUIFaZMdd/Cx9bRWAGZG087t5dUHJuMnVVcpHZFnHBKr8ag1eH/K tFdDFtyln5A/f9O22xsV0pyJni7e2z7lTBitrQFG69vnVGJlHbBE2dR4GddZqAlVOUbtEcE7 /aMk4TrCtx0IyOzQiLA81aaJWhkD3fRO8cDlR4YQ3F0aqjYy8x1EnnhhohHOwU0EVaN9oQEQ AMPNymBNoCWc13U6qOztXrIKBVsLGZXq/yOaR2n7gFbFACD0TU7XuH2UcnwvNR+uQFwSrRqa EczX2V6iIy2CITXKg5Yvg12yn09gTmafuoIyKoU16XvC3aZQQ2Bn3LO2sRP0j/NuMD9GlO37 pHCVRpI2DPxFE39TMm1PLbHnDG8+lZql+dpNwWw8dDaRgyXx2Le542CcTBT52VCeeWDtqd2M wOr4LioYlfGfAqmwcwucBdTEBUxklQaOR3VbJQx6ntI2oDOBlNGvjnVDzZe+iREd5l40l+Oj TaiWvBGXkv6OI+wx5TFPp+BM6ATU+6UzFRTUWbj+LqVA/JMqYHQp04Y4H5GtjbHCa8abRvBw IKEvpwTyWZlfXPtp8gRlNmxYn6gQlTyEZAWodXwE7CE+KxNnq7bPHeLvrSn8bLNK682PoTGr 0Y00bguYLfyvEwuDYek1/h9YSXtHaCR3CEj4LU1B561G1j7FVaeYbX9bKBAoy/GxAW8J5O1n mmw7FnkSHuwO/QDe0COoO0QZ620Cf9IBWYHW4m2M2yh5981lUaiMcNM2kPgsJFYloFo2XGn6 lWU9BrWjEoNDhHZtF+yaPEuwjZo6x/3E2Tu3E5Jj0VpVcE9U1Zq/fquDY79l2RJn5ENogOs5 +Pi0GjVpEYQVWfm0PTCxNPOzOzGR4QB3BNFvABEBAAHCwZMEGAEIACYCGwwWIQS/HfwKVo8F 95V1cJC9alAct4t8JgUCXk7nGAUJEhFq9wAhCRC9alAct4t8JhYhBL8d/ApWjwX3lXVwkL1q UBy3i3wmVBwP/RNNux3dC513quZ0hFyU6ZDTxbiafprLN2PXhmLslxPktJgW/xO5xp16OXkW YgNI/TKxj3+oSu+MhEAhAFA2urFWHyqedfqdndQTzbv4yqNuyhGupzPBWNSqqJ2NwKJc9f2R wqYTXVYIO+6KLa32rpl7xvJISkx06s70lItFJjyOf6Hn1y5RBMwQN9hP2YxLhYNO3rmlNSVy 7Z/r95lZTDnnUCuxBZxnjx/pMHJ8LZtKY0t7D0esA+zYGUrmoAGUpNWEBP+uSL+f8rhjSAL0 HgoRL39ixg5Bm0MzJn9z3or++Pl5bRnSvHy6OKh7rzTjCwaGoZD+6LHBwPFPlmInX1H+yHrX lu1uPAdqG5xcsZAZFTxBRMEnYu1yYebDSA9x+iulggMZQcWC2GvHCaKIpKcFY8XCxk7Hbl5c 8hcPKWOy16NLO6Y66Ws4kMedXuNUHe4zBLVlRbcYUdgT9Brw8nxmxu3KhEVsJkwOpXLUDuzo hQNfg9em95lpAK+VOTocke8PSESy3GbEtmoMueW3caSeDHb5dRP6WrndaYhEOzAA/KjuPU7J LMXOABOMIq+R38y7e2B3TnVDCrccdZDseFPUWmH0cGCGihH/j2UZG+PImrSDCh3h5MedVHGo sI62tmWm0q6lrljwSZmMZ30w1QaGmdFpI3Q6V+nZ7TZldI3x Message-ID: Date: Sat, 21 Mar 2020 20:26:23 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200320204308.411f8d68@nic.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-leds-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-leds@vger.kernel.org Hi Marek, On 3/20/20 8:43 PM, Marek Behun wrote: > Hi Jacek, > > I want to open the discussions about HW LED triggers again. > The last time (which was almost a year ago, sorry for that) I proposed > an API which used the same sysfs trigger file as for regular trigger > setting, but the HW triggers were prefixed with "hw:" (and each LED > classdev can have different ones). > > You wrote: > >> I wonder what will be the gain of having hw triggers incorporated >> into LED trigger mechanism, if they are meant not be generic >> by design? Only the LED class driver exposing a hw trigger >> will know how to set it up, and will define protocol via which >> the settings will be passed from sysfs to the trigger (const char* >> parameter in the hw_trigger_set() op). >> >> And it has to be that way because hardware triggers are hardware >> specific. LED class driver will have to create trigger specific >> sysfs files regardless of whether they are to be shown on >> trigger avtivation, or will persist for the whole LED class device >> lifetime. >> >> Maybe I'm missing some vital details from the previous discussions, >> but this is what's come to my mind now, after analyzing the proposed >> design. >> >> The question is: what problem we solve by exposing non-generic >> hw trigger, whose implementation will be in the driver anyway, >> instead of just bypassing the trigger mechanism and exposing >> the required interface directly? > > I would still like to go this way, so my answer to this questions is: > - IMO this is simpler for users and existing scripts > - the idea is that it should no be possible to set a software trigger > and a hardware trigger at the same time (this would just end up in > more complications), and introducing special hw_trigger file or > something could make users think that you can OK, that seems like a decent justification. If you had provided it at that time then maybe we would have had generic hw trigger mechanism merged a year ago :-). -- Best regards, Jacek Anaszewski