On Thu, 27 Aug 2020 11:53:44 +0300 Alexandru Ardelean <ardeleanalex@xxxxxxxxx> wrote: > On Thu, Aug 27, 2020 at 9:57 AM Krzysztof Kozlowski <krzk@xxxxxxxxxx> wrote: > > > > On Wed, Aug 26, 2020 at 04:22:03PM +0300, Alexandru Ardelean wrote: > > > From: Sergiu Cuciurean <sergiu.cuciurean@xxxxxxxxxx> > > > > > > As part of the general cleanup of indio_dev->mlock, this change replaces > > > it with a local lock, to protect potential concurrent access to the > > > completion callback during a conversion. > > > > I don't know the bigger picture (and no links here for general cleanup) > > but I assume it is part of wider work and that mlock is unwanted. In > > such case: > > > > Reviewed-by: Krzysztof Kozlowski <krzk@xxxxxxxxxx> > > > > If it is part of some bigger work, please put a link to lore.kernel.org > > under separators ---, so everyone can get the context. > > Will keep that in mind. > I am not sure if there is a lore.kernel.org link that's easy to find > for a discussion on this topic, maybe I can describe it here and use > the link [from this later]. > > This was something that popped up during reviews we got from Jonathan > [or others], saying "please don't use indio_dev->mlock, that is an IIO > framework lock, and an IIO driver should not use it". Shortest one is the docs for that lock say don't use it directly in a driver :) https://elixir.bootlin.com/linux/latest/source/include/linux/iio/iio.h#L495 > Reasons include [and some may be repeated a bit]: > - this could cause a deadlock if the IIO framework holds this lock and > an IIO driver also tries to get a hold of this lock > - similar to the previous point, this mlock is taken by > iio_device_claim_direct_mode() and released by > iio_device_release_direct_mode() ; which means that mlock aims to > become more of an IIO framework lock, than a general usage lock; > - this wasn't policed/reviewed intensely in the older driver [a few > years ago], but has become a point in recent reviews; > - if we want to develop/enhance the IIO framework, some elements like > this need to be taken care of, as more drivers get added and more > complexity gets added; One side note here is we want to make all this [INTERN] state in struct iio_dev opaque to drivers. It'll take a while as the boundary gets crossed in various drivers. > - there is an element of fairness [obviously], where someone writing a > new IIO driver, takes an older one as example, and gets hit on the > review; the person feels they did a good job in mimicking the old > driver; their feeling is correct; the IIO framework should provide > good references and/or cleanup existing drivers; > - same as the previous point, we don't want to keep telling people > writing new IIO drivers [and starting out with IIO] to "not use mlock > [because it was copied from an old driver]"; it's more/needless review > work Good explanation. Thanks, Jonathan > > > > > > > > Best regards, > > Krzysztof > > > > > > > > Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@xxxxxxxxxx> > > > Signed-off-by: Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx> > > > --- > > > drivers/iio/adc/exynos_adc.c | 12 ++++++++---- > > > 1 file changed, 8 insertions(+), 4 deletions(-) > > >
