On Wed, Jan 27, 2021 at 8:56 AM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: > > Hi Saravana, > > On Wed, Jan 27, 2021 at 5:42 PM Saravana Kannan <saravanak@xxxxxxxxxx> wrote: > > On Tue, Jan 26, 2021 at 11:43 PM Geert Uytterhoeven > > <geert@xxxxxxxxxxxxxx> wrote: > > > On Wed, Jan 27, 2021 at 1:44 AM Saravana Kannan <saravanak@xxxxxxxxxx> wrote: > > > > On Tue, Jan 26, 2021 at 12:50 AM Geert Uytterhoeven > > > > <geert@xxxxxxxxxxxxxx> wrote: > > > > > On Mon, Jan 25, 2021 at 11:42 PM Saravana Kannan <saravanak@xxxxxxxxxx> wrote: > > > > > > On Mon, Jan 25, 2021 at 11:49 AM Michael Walle <michael@xxxxxxxx> wrote: > > > > > > > Am 2021-01-21 12:01, schrieb Geert Uytterhoeven: > > > > > > > > On Thu, Jan 21, 2021 at 1:05 AM Saravana Kannan <saravanak@xxxxxxxxxx> > > > > > > > > wrote: > > > > > > > >> On Wed, Jan 20, 2021 at 3:53 PM Michael Walle <michael@xxxxxxxx> > > > > > > > >> wrote: > > > > > > > >> > Am 2021-01-20 20:47, schrieb Saravana Kannan: > > > > > > > >> > > On Wed, Jan 20, 2021 at 11:28 AM Michael Walle <michael@xxxxxxxx> > > > > > > > >> > > wrote: > > > > > > > >> > >> > > > > > > > >> > >> [RESEND, fat-fingered the buttons of my mail client and converted > > > > > > > >> > >> all CCs to BCCs :(] > > > > > > > >> > >> > > > > > > > >> > >> Am 2021-01-20 20:02, schrieb Saravana Kannan: > > > > > > > >> > >> > On Wed, Jan 20, 2021 at 6:24 AM Rob Herring <robh@xxxxxxxxxx> wrote: > > > > > > > >> > >> >> > > > > > > > >> > >> >> On Wed, Jan 20, 2021 at 4:53 AM Michael Walle <michael@xxxxxxxx> > > > > > > > >> > >> >> wrote: > > > > > > > >> > >> >> > > > > > > > > >> > >> >> > fw_devlink will defer the probe until all suppliers are ready. We can't > > > > > > > >> > >> >> > use builtin_platform_driver_probe() because it doesn't retry after probe > > > > > > > >> > >> >> > deferral. Convert it to builtin_platform_driver(). > > > > > > > >> > >> >> > > > > > > > >> > >> >> If builtin_platform_driver_probe() doesn't work with fw_devlink, then > > > > > > > >> > >> >> shouldn't it be fixed or removed? > > > > > > > >> > >> > > > > > > > > >> > >> > I was actually thinking about this too. The problem with fixing > > > > > > > >> > >> > builtin_platform_driver_probe() to behave like > > > > > > > >> > >> > builtin_platform_driver() is that these probe functions could be > > > > > > > >> > >> > marked with __init. But there are also only 20 instances of > > > > > > > >> > >> > builtin_platform_driver_probe() in the kernel: > > > > > > > >> > >> > $ git grep ^builtin_platform_driver_probe | wc -l > > > > > > > >> > >> > 20 > > > > > > > >> > >> > > > > > > > > >> > >> > So it might be easier to just fix them to not use > > > > > > > >> > >> > builtin_platform_driver_probe(). > > > > > > > >> > >> > > > > > > > > >> > >> > Michael, > > > > > > > >> > >> > > > > > > > > >> > >> > Any chance you'd be willing to help me by converting all these to > > > > > > > >> > >> > builtin_platform_driver() and delete builtin_platform_driver_probe()? > > > > > > > >> > >> > > > > > > > >> > >> If it just moving the probe function to the _driver struct and > > > > > > > >> > >> remove the __init annotations. I could look into that. > > > > > > > >> > > > > > > > > > >> > > Yup. That's pretty much it AFAICT. > > > > > > > >> > > > > > > > > > >> > > builtin_platform_driver_probe() also makes sure the driver doesn't ask > > > > > > > >> > > for async probe, etc. But I doubt anyone is actually setting async > > > > > > > >> > > flags and still using builtin_platform_driver_probe(). > > > > > > > >> > > > > > > > > >> > Hasn't module_platform_driver_probe() the same problem? And there > > > > > > > >> > are ~80 drivers which uses that. > > > > > > > >> > > > > > > > >> Yeah. The biggest problem with all of these is the __init markers. > > > > > > > >> Maybe some familiar with coccinelle can help? > > > > > > > > > > > > > > > > And dropping them will increase memory usage. > > > > > > > > > > > > > > Although I do have the changes for the builtin_platform_driver_probe() > > > > > > > ready, I don't think it makes much sense to send these unless we agree > > > > > > > on the increased memory footprint. While there are just a few > > > > > > > builtin_platform_driver_probe() and memory increase _might_ be > > > > > > > negligible, there are many more module_platform_driver_probe(). > > > > > > > > > > > > While it's good to drop code that'll not be used past kernel init, the > > > > > > module_platform_driver_probe() is going even more extreme. It doesn't > > > > > > even allow deferred probe (well before kernel init is done). I don't > > > > > > think that behavior is right and that's why we should delete it. Also, > > > > > > > > > > This construct is typically used for builtin hardware for which the > > > > > dependencies are registered very early, and thus known to probe at > > > > > first try (if present). > > > > > > > > > > > I doubt if any of these probe functions even take up 4KB of memory. > > > > > > > > > > How many 4 KiB pages do you have in a system with 10 MiB of SRAM? > > > > > How many can you afford to waste? > > > > > > > > There are only a few instances of this macro in the kernel. How many > > > > > > $ git grep -lw builtin_platform_driver_probe | wc -l > > > 21 > > > $ git grep -lw module_platform_driver_probe | wc -l > > > 86 > > > > > > + the ones that haven't been converted to the above yet: > > > > > > $ git grep -lw platform_driver_probe | wc -l > > > 58 > > > > > > > Yeah, this adds up in terms of the number of places we'd need to fix. > > But thinking more about it, a couple of points: > > 1. Not all builtin_platform_driver_probe() are problems for > > fw_devlink. So we can just fix them as we go if we need to. > > > > 2. The problem with builtin_platform_driver_probe() isn't really with > > the use of __init. It's the fact that it doesn't allow deferred > > probes. builtin_platform_driver_probe()/platform_driver_probe() could > > still be fixed up to allow deferred probe until we get to the point > > where we free the __init section (so at least till late_initcall). > > That's intentional: it is used for cases that will (must) never be deferred. > That's why it's safe to use __init. So was the usage of builtin_platform_driver_probe() wrong in the driver Michael fixed? Because, deferring and probing again clearly works? Also, "must never be deferred" seems like a weird condition to enforce. I think the real "rule" is that if it defers, the platform is not expected to work. But disallowing a probe reattempt seems weird. What is it going to hurt if it's attempted again? At worst it fails one more time? Also, I'd argue that all/most of the "can't defer, but I'm still a proper struct device" cases are all just patchwork to deal with the fact we were playing initcall chicken when there was no fw_devlink. I'm hoping we can move people away from that mindset. And the first step towards that would be to allow *platform_probe() to allow deferred probes until late_initcall(). -Saravana
