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Date: Tue, 30 Jun 2020 11:08:37 +0200 From: Bartosz Golaszewski <bgolaszewski@...libre.com> To: Kent Gibson <warthog618@...il.com> Cc: LKML <linux-kernel@...r.kernel.org>, linux-gpio <linux-gpio@...r.kernel.org>, Linus Walleij <linus.walleij@...aro.org> Subject: Re: [PATCH 08/22] gpiolib: cdev: complete the irq/thread timestamp handshake On Thu, Jun 25, 2020 at 12:01 PM Kent Gibson <warthog618@...il.com> wrote: > > On Thu, Jun 25, 2020 at 11:44:30AM +0200, Bartosz Golaszewski wrote: > > On Wed, Jun 24, 2020 at 4:08 PM Kent Gibson <warthog618@...il.com> wrote: > > > > > > On Wed, Jun 24, 2020 at 04:00:42PM +0200, Bartosz Golaszewski wrote: > > > > wt., 23 cze 2020 o 06:02 Kent Gibson <warthog618@...il.com> napisaĆ(a): > [ snip ] > > > > > > I'm not totally sure myself, as my understanding of how interrupts are > > > shared in the kernel is pretty sketchy, but my concern is that if we > > > are sharing the irq then whoever we are sharing with may release the irq > > > and we go from nested to unnested. Or vice versa. Not sure if that is > > > valid, but that was my concern, and it seemed like a minor change to > > > cover it just in case. > > > > > > > It's my understanding that a shared interrupt must be explicitly > > requested as shared by all previous users or request_irq() will fail. > > In this case: we call request_threaded_irq() without the IRQF_SHARED > > flag so it's never a shared interrupt. Even if someone previously > > requested it as shared - our call will simply fail. > > > > OK. Is there a reason not to share the interrupt? > If nobody requested this yet, I'd say: let's not touch it. :) In theory, we check if the line state changed so we should be fine but in practice this sounds like a can of worms. That being said: I don't have a reason not to do it. Just a feeling. > > I still think that resetting the timestamp is fine because it's not > > being set to 0 in hardirq context. We just need a different > > explanation. > > > > Or just drop it? Yes, I think dropping this patch for now is fine. Bart
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