From: plagnioj@jcrosoft•com (Jean-Christophe PLAGNIOL-VILLARD)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH RESEND 1/5 v6] gpio: Add a block GPIO API to gpiolib
Date: Thu, 1 Nov 2012 15:44:07 +0100 [thread overview]
Message-ID: <20121101144407.GG19021@game.jcrosoft.org> (raw)
In-Reply-To: <CACxGe6vEr5fd0_ZuzV=nOXVfwA7_FB5L6KJsEwMEHmVj0rDA=g@mail.gmail.com>
On 19:59 Wed 31 Oct , Grant Likely wrote:
> Hi Roland
>
> On Wed, Oct 31, 2012 at 6:19 PM, Roland Stigge <stigge@antcom•de> wrote:
> > On 10/31/2012 04:00 PM, Grant Likely wrote:
> >> For the API, I don't think it is a good idea at all to try and
> >> abstract away gpios on multiple controllers. I understand that it
> >> makes life a lot easier for userspace to abstract those details away,
> >> but the problem is that it hides very important information about how
> >> the system is actually constructed that is important to actually get
> >> things to work. For example, say you have a gpio-connected device with
> >> the constraint that GPIOA must change either before or at the same
> >> time as GPIOB, but never after. If those GPIOs are on separate
> >> controllers, then the order is completely undefined
> >
> > It is correct that it's not (yet) well documented and the API is also
> > not very explicit about it, but the actual approach of the manipulation
> > order is to let drivers handle gpios "as simultaneous as possible" and
> > when not possible, do it in the _order of bits specified_ (either
> > defined at the device tree level, or when created via
> > block_gpio_create() directly).
>
> The documentation is actually fine. I do understand that the intent is
> "as simultaneous as possible", but I accept the point that the order
> of specification affects the behaviour*. However, it still remains
> that the method used by the ABI abstracts at the wrong level and that
> blocking arbitrary GPIO pins into a single virtual GPIO register is a
> bad idea.
>
> *note that the current code doesn't implement that intended behaviour
> either since the gpios are processed in the order of the controllers,
> not the order of the bits.
>
> > I'm not sure how far you tested the API in depth: You can already define
> > a block that maps onto a subset of gpios on a controller and internally
> > of course maps onto those set and clear operations. Whenever you need to
> > manipulate a different subset (whether disjoint or overlapping), you can
> > easily define _additional_ blocks. From my experience, this solves most
> > of the real world problems when n-bit busses are bit banged over GPIOs.
> > Doesn't this already solve this (in a different way, though)?
>
> Blech! Requiring a new block for each possible combination of
> write-at-once bits is a horrible ABI. That just strengthens my opinion
> that the abstraction isn't right yet.
>
> > Pin direction currently needs to be set up separately, analogous to
> > requesting gpios. Need to document this better, right. The assumption is
> > that I/O needs to be efficient primarily, before bloating the API with
> > direction functions. Or should I add functions for this?
>
> Since this is a userspace facing ABI, once it is merged it cannot be
> changed in an incompatible way. I cannot merge it until there is at
> least a plan for how to handle all of the reasonable use cases. That
> means it must support set/clear or mask operations. Also, if it sticks
> with the design of grouping pins from multiple controllers, then it
> needs to handle explicitly constraining what order operations are
> performed in at the time of the operation. At the time of setup
> doesn't work since constraints between pins may not always be in the
> same order.
>
> I really think you should consider implementing a command stream type
> of interface.
I agreed with Grant and I'm not also a fan of the sysfs ABI
as I already point out in the previous version and Linus too
Best Regards,
J.
>
> g.
next prev parent reply other threads:[~2012-11-01 14:44 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-28 20:46 [PATCH RESEND 0/5 v6] gpio: Add block GPIO Roland Stigge
2012-10-28 20:46 ` [PATCH RESEND 1/5 v6] gpio: Add a block GPIO API to gpiolib Roland Stigge
2012-10-31 14:06 ` Linus Walleij
2012-10-31 17:47 ` Roland Stigge
2012-10-31 15:00 ` Grant Likely
2012-10-31 17:19 ` Roland Stigge
2012-10-31 18:59 ` Grant Likely
2012-11-01 14:44 ` Jean-Christophe PLAGNIOL-VILLARD [this message]
2012-11-02 9:22 ` Roland Stigge
2012-10-31 19:30 ` Mark Brown
2012-11-01 15:14 ` Grant Likely
2012-10-28 20:46 ` [PATCH RESEND 2/5 v6] gpio: Add sysfs support to block GPIO API Roland Stigge
2012-10-28 20:46 ` [PATCH RESEND 3/5 v6] gpiolib: Fix default attributes for class Roland Stigge
2012-10-31 15:04 ` Grant Likely
2012-10-28 20:46 ` [PATCH RESEND 4/5 v6] gpio: Add device tree support to block GPIO API Roland Stigge
2012-10-31 15:05 ` Grant Likely
2012-10-28 20:46 ` [PATCH RESEND 5/5 v6] gpio: Add block gpio to several gpio drivers Roland Stigge
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