On Thu, Apr 28, 2022 at 02:11:31PM -0400, Paul Gortmaker wrote: > [Re: [PATCH 0/4] platform: allow ATOM PMC code to be optional] On 28/04/2022 (Thu 13:12) Andy Shevchenko wrote: > > On Thu, Apr 28, 2022 at 02:24:26AM -0400, Paul Gortmaker wrote: > > > A few months back I was doing a test build for "defconfig-like" COTS > > > hardware and happened to notice some pmc-atom stuff being built. Fine, > > > I thought - the defconfig isn't minimal - we all know that - what Kconfig > > > do I use to turn that off? Well, imagine my surprise when I found out > > > you couldn't turn it [Atom Power Management Controller] code off! > > > > Turning it off on BayTrail and CherryTrail devices will be devastating > > to the users' experience. And plenty of cheap tablets are exactly made > > on that SoCs. > > Sure, but I could say the same thing for DRM_I915 and millions of > desktop PC users - yet we still give all the other non i915 users the > option to be able to turn it off. Pick any other Kconfig value you like > and the same thing holds true. > > Just so we are on the same page - I want to give the option to let > people opt out, and at the same time not break existing users. If you > think the defconfig default of being off is too risky, then I am OK with > that and we can just start by exposing the option with "default y". > > So, to that end - are you OK with exposing the Kconfig so people can > opt out, or are you 100% against exposing the Kconfig at all? That > obviously has the most impact on what I do or don't do next. > > > > Normally we all agree to not use "default y" unless unavoidable, but > > > somehow this was added as "def_bool y" which is even worse ; you can > > > see the Kconfig setting but there is *no* way you can turn it off. > > > > > > After investigating, I found no reason why the atom code couldn't be > > > opt-out with just minor changes that the original addition overlooked. > > > > > > And so this series addreses that. I tried to be sensitive to not > > > break any existing configs in the process, but the defconfig will > > > now intentionally be different and exclude this atom specific code. > > > > > > Using a defconfig on today's linux-next, here is the delta summary: > > > > > > $ ./scripts/bloat-o-meter -c ../pmc-atom-pre/vmlinux ../pmc-atom-post/vmlinux|grep add/remove > > > add/remove: 0/410 grow/shrink: 0/7 up/down: 0/-47659 (-47659) > > > add/remove: 0/105 grow/shrink: 0/1 up/down: 0/-6848 (-6848) > > > add/remove: 0/56 grow/shrink: 0/1 up/down: 0/-10155 (-10155) > > > > > > $ ./scripts/bloat-o-meter -c ../pmc-atom-pre/vmlinux ../pmc-atom-post/vmlinux|grep Total > > > Total: Before=13626994, After=13579335, chg -0.35% > > > Total: Before=3572137, After=3565289, chg -0.19% > > > Total: Before=1235335, After=1225180, chg -0.82% > > > > > > It is hard to reclaim anything against the inevitable growth in > > > footprint, so I'd say we should be glad to take whatever we can. > > > > > > Boot tested defconfig on today's linux-next on older non-atom COTS. > > > > I believe this needs an extensive test done by Hans who possesses a lot of > > problematic devices that require that module to be present. > > Input from Hans is 100% welcome - but maybe again if we just consider > using "default y" even though it isn't typical - then your concerns are > not as extensive? > > > Note to all your patches, please, use --cc option instead of putting noisy > > lines in the each of the commit messages. For myself I created a "smart" > > script [1] to avoid bothering with that. Feel free to use, modify, send PRs > > back to improve. > > Thanks - I'm used to explicitly capturing who was looped into the > discussion. But I hadn't considered how things have evolved so that in > certain circumstances that might be considered just noise with the wider > audience we see in the typical patch sets of today. > > Assuming you are OK with exposing the option as a choice, I'll make > things "default y" in v2 to ensure we've minimized risk to existing > users who rely on it, but wait a while for others like Hans to put in > their input. I'll probably follow up in the individual patches to ask > for clarification if I'm not clear on what you had in mind. My main concern is the existing users' experience. Opting-out the option is a good to have, I'm not against it. -- With Best Regards, Andy Shevchenko
