From: Kent Gibson <firstname.lastname@example.org> To: Bartosz Golaszewski <email@example.com> Cc: LKML <firstname.lastname@example.org>, linux-gpio <email@example.com>, Linus Walleij <firstname.lastname@example.org> Subject: Re: [PATCH v2 02/18] gpio: uapi: define uAPI v2 Date: Thu, 6 Aug 2020 09:03:30 +0800 Message-ID: <20200806010330.GA11890@sol> (raw) In-Reply-To: <CAMpxmJWWmBULX+RdqN3nyXFO4M9sbu2Q6i11UJMiKxomVDr47g@mail.gmail.com> On Wed, Aug 05, 2020 at 07:47:57PM +0200, Bartosz Golaszewski wrote: > On Wed, Aug 5, 2020 at 7:19 AM Kent Gibson <email@example.com> wrote: > > > > [snip] > > > > > > > > > +/* > > > > + * Maximum number of requested lines. > > > > + * > > > > + * Must be a multiple of 8 to ensure 32/64-bit alignment of structs. > > > > + */ > > > > +#define GPIOLINES_MAX 64 > > > > + > > > > +/* The number of __u64 required for a bitmap for GPIOLINES_MAX lines */ > > > > +#define GPIOLINES_BITMAP_SIZE __KERNEL_DIV_ROUND_UP(GPIOLINES_MAX, 64) > > > > + > > > > > > In what circumstances can this be different than 1? It's worth > > > documenting here I suppose. > > > > > > > In terms of the API definition, GPIOLINES_MAX can be anything you want > > and the definitions are still valid. In practice in the mainline kernel > > it would always be 1 for ABI compatibility. > > > > Chiselling GPIOLINES_MAX <= 64 into stone could simplify things a bit, > > as all the bitmaps reduce to a single __u64. Would you prefer that? > > > > I'm not sure I follow. We need to chisel some max value in stone. Up > to that point it's been 64. We can make it more and the bitmap API > would handle it alright but if we don't, then this > __KERNEL_DIV_ROUND_UP() is unnecessary. Limiting it to 64 makes things > very simple thanks to fitting into a __u64 though. I've personally > never needed to request even half that so I guess this value's fine? > By "chiselling in stone" I mean not supporting > 64 lines - even in custom kernel builds. The uAPI and definition and implementation would lock that in. As it stands a custom build could use > 64 and it should all still work as the bitmaps would be resized. I satisfied that 64 is more than enough for what this API is intended for, so I'll change the bitmaps to a single __u64, and remove GPIOLINES_BITMAP_SIZE. [ snip] > > > > + __u64 bits[GPIOLINES_BITMAP_SIZE]; > > > > +}; > > > > + > > > > > > We can set values only for a subset of requested lines but AFAICT we > > > can't read values of only a subset of lines. Would it be difficult to > > > remove this limitation? While reading values always succeeds - even if > > > the line is in input mode and has edge detected - I think that someone > > > may want to request the max number of lines without reading all their > > > values each time. Maybe consider merging this with struct > > > gpioline_set_values? > > > > > > > That is correct. > > > > I considered that corner case to be unlikely, as a major point of > > requesting lines together is to be able to perform collective operations > > on them as atomically as possible. If you only want subsets then > > request them as separate subsets. > > > > And yet this version implements heterogeneous config and setting edge > detection and values of subsets of requested lines. :) > The corner case I was referring to was only wanting to get a subset of lines and caring that there may be a slight performance gain if the kernel filters out the lines you aren't interested in :(. > > Do you have a case in mind where you would have overlapping subsets? > > > > No, not really but then I also don't have a use-case for setting only > a certain subset of lines. > > > Not difficult to remove the limitation - I just didn't see sufficient > > benefit. > > > > Using the same structure for setting and getting values is a benefit > IMO. If it's not a difficult task, then I think it's worth adding it. > OK, will add it in. [ snip] > > > (maybe even define a special macro to set all bits in mask - > > > GPIOLINE_CONFIG_ALL_LINES or something) on a first-in-wins basis. I'm > > > open to other suggestions though. > > > > > > > I think I've addressed this elsewhere, and still think it is worthwhile > > and very low cost. I thought it was an easy win when I added it, and > > still do. > > > > Happy to change the attrs to first-in-wins though - the validation of > > the attrs is still my biggest bugbear with this version. > > Yes, I read your other reply. Ok, makes sense to have default flags > with an attribute for overrides. This just needs very explicit > documentation. > I'll add documentation that the attrs associations are on a first-in-wins basis, and that subsequent associations are ignored. Cheers, Kent.
next prev parent reply index Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-07-25 4:19 [PATCH v2 00/18] gpio: cdev: add uAPI V2 Kent Gibson 2020-07-25 4:19 ` [PATCH v2 01/18] gpio: uapi: define GPIO_MAX_NAME_SIZE for array sizes Kent Gibson 2020-07-25 4:19 ` [PATCH v2 02/18] gpio: uapi: define uAPI v2 Kent Gibson 2020-08-04 17:42 ` Bartosz Golaszewski 2020-08-05 5:18 ` Kent Gibson 2020-08-05 17:47 ` Bartosz Golaszewski 2020-08-06 1:03 ` Kent Gibson [this message] 2020-08-06 1:15 ` Kent Gibson 2020-08-06 15:53 ` Bartosz Golaszewski 2020-07-25 4:19 ` [PATCH v2 03/18] gpiolib: make cdev a build option Kent Gibson 2020-07-25 20:29 ` Andy Shevchenko 2020-07-26 22:25 ` Linus Walleij 2020-07-27 1:46 ` Kent Gibson 2020-07-27 5:57 ` Kent Gibson 2020-07-27 8:15 ` Linus Walleij 2020-07-25 4:19 ` [PATCH v2 04/18] gpiolib: add build option for CDEV v1 ABI Kent Gibson 2020-07-25 4:19 ` [PATCH v2 05/18] gpiolib: cdev: support GPIO_GET_LINE_IOCTL and GPIOLINE_GET_VALUES_IOCTL Kent Gibson 2020-07-25 20:51 ` Andy Shevchenko 2020-07-26 1:12 ` Kent Gibson 2020-07-26 3:24 ` Kent Gibson 2020-07-29 2:28 ` Kent Gibson 2020-07-29 8:05 ` Andy Shevchenko 2020-07-29 10:01 ` Kent Gibson 2020-07-31 16:05 ` Bartosz Golaszewski 2020-08-02 3:31 ` Kent Gibson 2020-08-02 9:32 ` Kent Gibson 2020-08-03 19:59 ` Bartosz Golaszewski 2020-08-03 20:02 ` Bartosz Golaszewski 2020-08-03 23:01 ` Kent Gibson 2020-08-04 17:47 ` Bartosz Golaszewski 2020-08-05 3:06 ` Kent Gibson 2020-07-25 4:19 ` [PATCH v2 06/18] gpiolib: cdev: support GPIO_GET_LINEINFO_V2_IOCTL and GPIO_GET_LINEINFO_WATCH_V2_IOCTL Kent Gibson 2020-07-25 4:19 ` [PATCH v2 07/18] gpiolib: cdev: support edge detection for uAPI v2 Kent Gibson 2020-08-04 19:28 ` Bartosz Golaszewski 2020-07-25 4:19 ` [PATCH v2 08/18] gpiolib: cdev: support GPIOLINE_SET_CONFIG_IOCTL Kent Gibson 2020-07-25 4:19 ` [PATCH v2 09/18] gpiolib: cdev: support GPIOLINE_SET_VALUES_IOCTL Kent Gibson 2020-07-25 4:19 ` [PATCH v2 10/18] gpiolib: cdev: support setting debounce Kent Gibson 2020-07-25 4:19 ` [PATCH v2 11/18] gpio: uapi: document uAPI v1 as deprecated Kent Gibson 2020-08-04 19:43 ` Bartosz Golaszewski 2020-07-25 4:19 ` [PATCH v2 12/18] tools: gpio: port lsgpio to v2 uAPI Kent Gibson 2020-07-25 4:19 ` [PATCH v2 13/18] tools: gpio: port gpio-watch " Kent Gibson 2020-07-25 4:19 ` [PATCH v2 14/18] tools: gpio: rename nlines to num_lines Kent Gibson 2020-07-25 4:19 ` [PATCH v2 15/18] tools: gpio: port gpio-hammer to v2 uAPI Kent Gibson 2020-07-25 4:19 ` [PATCH v2 16/18] tools: gpio: port gpio-event-mon " Kent Gibson 2020-07-25 4:19 ` [PATCH v2 17/18] tools: gpio: add debounce support to gpio-event-mon Kent Gibson 2020-07-25 4:19 ` [PATCH v2 18/18] tools: gpio: add multi-line monitoring " Kent Gibson
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