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[91.78.208.152]) by smtp.googlemail.com with ESMTPSA id j13sm11409029lfb.19.2020.04.27.08.18.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 27 Apr 2020 08:18:35 -0700 (PDT) Subject: Re: [PATCH v2 1/2] i2c: tegra: Better handle case where CPU0 is busy for a long time To: Thierry Reding Cc: Jon Hunter , Wolfram Sang , Laxman Dewangan , Manikanta Maddireddy , Vidya Sagar , linux-i2c@vger.kernel.org, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org References: <79f6560e-dbb5-0ae1-49f8-cf1cd95396ec@nvidia.com> <20200427074837.GC3451400@ulmo> <20200427110033.GC3464906@ulmo> <3a06811c-02dc-ce72-ebef-78c3fc3f4f7c@gmail.com> <20200427151234.GE3464906@ulmo> From: Dmitry Osipenko Message-ID: <1ab276cf-c2b0-e085-49d8-b8ce3dba8fbe@gmail.com> Date: Mon, 27 Apr 2020 18:18:34 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200427151234.GE3464906@ulmo> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-i2c-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-i2c@vger.kernel.org 27.04.2020 18:12, Thierry Reding пишет: > On Mon, Apr 27, 2020 at 05:21:30PM +0300, Dmitry Osipenko wrote: >> 27.04.2020 14:00, Thierry Reding пишет: >>> On Mon, Apr 27, 2020 at 12:52:10PM +0300, Dmitry Osipenko wrote: >>>> 27.04.2020 10:48, Thierry Reding пишет: >>>> ... >>>>>> Maybe but all these other problems appear to have existed for sometime >>>>>> now. We need to fix all, but for the moment we need to figure out what's >>>>>> best for v5.7. >>>>> >>>>> To me it doesn't sound like we have a good handle on what exactly is >>>>> going on here and we're mostly just poking around. >>>>> >>>>> And even if things weren't working quite properly before, it sounds to >>>>> me like this patch actually made things worse. >>>> >>>> There is a plenty of time to work on the proper fix now. To me it sounds >>>> like you're giving up on fixing the root of the problem, sorry. >>> >>> We're at -rc3 now and I haven't seen any promising progress in the last >>> week. All the while suspend/resume is now broken on at least one board >>> and that may end up hiding any other issues that could creep in in the >>> meantime. >>> >>> Furthermore we seem to have a preexisting issue that may very well >>> interfere with this patch, so I think the cautious thing is to revert >>> for now and then fix the original issue first. We can always come back >>> to this once everything is back to normal. >>> >>> Also, people are now looking at backporting this to v5.6. Unless we >>> revert this from v5.7 it may get picked up for backports to other >>> kernels and then I have to notify stable kernel maintainers that they >>> shouldn't and they have to back things out again. That's going to cause >>> a lot of wasted time for a lot of people. >>> >>> So, sorry, I disagree. I don't think we have "plenty of time". >> >> There is about a month now before the 5.7 release. It's a bit too early >> to start the panic, IMO :) > > There's no panic. A patch got merged and it broken something, so we > revert it and try again. It's very much standard procedure. > >> Jon already proposed a reasonable simple solution: to keep PCIe >> regulators always-ON. In a longer run we may want to have I2C atomic >> transfers supported for a late suspend phase. > > That's not really a solution, though, is it? It's just papering over > an issue that this patch introduced or uncovered. I'm much more in > favour of fixing problems at the root rather than keep papering over > until we loose track of what the actual problems are. It's not "papering over an issue". The bug can't be fixed properly without introducing I2C atomic transfers support for a late suspend phase, I don't see any other solutions for now. Stable kernels do not support atomic transfers at all, that proper solution won't be backportable.