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[220.235.109.115]) by smtp.gmail.com with ESMTPSA id w7sm2041793pfb.101.2019.11.20.23.46.23 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 20 Nov 2019 23:46:25 -0800 (PST) Date: Thu, 21 Nov 2019 15:46:21 +0800 From: Kent Gibson To: Bartosz Golaszewski Cc: Bartosz Golaszewski , linux-gpio Subject: Re: [libgpiod] [PATCH 11/19] API: add support for SET_CONFIG Message-ID: <20191121074621.GA17026@sol> References: <20191119155249.GA20834@sol> <20191120135857.GA4218@sol> <20191120141353.GA5154@sol> <20191120143644.GA5865@sol> <20191121003443.GA7695@sol> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-gpio-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-gpio@vger.kernel.org On Thu, Nov 21, 2019 at 08:13:42AM +0100, Bartosz Golaszewski wrote: > czw., 21 lis 2019 o 01:34 Kent Gibson napisał(a): > > > > On Wed, Nov 20, 2019 at 04:18:24PM +0100, Bartosz Golaszewski wrote: > > > śr., 20 lis 2019 o 15:36 Kent Gibson napisał(a): > > > > > > > > On Wed, Nov 20, 2019 at 03:18:36PM +0100, Bartosz Golaszewski wrote: > > > > > śr., 20 lis 2019 o 15:13 Kent Gibson napisał(a): > > > > > > > > > > > > On Wed, Nov 20, 2019 at 03:08:57PM +0100, Bartosz Golaszewski wrote: > > > > > > > śr., 20 lis 2019 o 14:59 Kent Gibson napisał(a): > > > > > > > > > > > > > > > > On Wed, Nov 20, 2019 at 12:00:45PM +0100, Bartosz Golaszewski wrote: > > > > > > > > > wt., 19 lis 2019 o 16:53 Kent Gibson napisał(a): > > > > > > > > > > > > > > > > > > > > On Mon, Nov 18, 2019 at 10:48:25PM +0800, Kent Gibson wrote: > > > > > > > > > > > On Mon, Nov 18, 2019 at 02:52:04PM +0100, Bartosz Golaszewski > > > > > > > > > > > > > + > > > > > > > > > > > > > +int gpiod_line_set_flags_bulk(struct gpiod_line_bulk *bulk, int flags) > > > > > > > > > > > > > +{ > > > > > > > > > > > > > + struct gpiod_line *line; > > > > > > > > > > > > > + int values[GPIOD_LINE_BULK_MAX_LINES]; > > > > > > > > > > > > > + unsigned int i; > > > > > > > > > > > > > + int direction; > > > > > > > > > > > > > + > > > > > > > > > > > > > + line = gpiod_line_bulk_get_line(bulk, 0); > > > > > > > > > > > > > + if (line->as_is) { > > > > > > > > > > > > > > > > > > > > > > > > Can you explain the purpose of this as_is field? I'm not sure this is > > > > > > > > > > > > really needed. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > It is there for gpiod_set_flags, which has to populate the direction > > > > > > > > > > > flags in the SET_CONFIG ioctl. The existing line->direction is > > > > > > > > > > > either input or output. It is drawn from GPIOLINE_FLAG_IS_OUT, so > > > > > > > > > > > as-is is gets mapped to input. > > > > > > > > > > > I didn't want to change the existing line->direction, and adding the > > > > > > > > > > > as-is seemed clearer than adding another flavour of direction that > > > > > > > > > > > contained all three. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Hmmm, I think I see what you were getting at - the line->direction is the > > > > > > > > > > direction from the kernel, so it doesn't hurt to use that value to set the > > > > > > > > > > corresponding request flags - even if the original request was as-is?? > > > > > > > > > > > > > > > > > > > > If that is the case then the line->as_is can be dropped throughout. > > > > > > > > > > > > > > > > > > > > Kent. > > > > > > > > > > > > > > > > > > > > > > > > > > > > Yes, this is what I was thinking. Just need to make sure the value > > > > > > > > > from the kernel is up-to-date. > > > > > > > > > > > > > > > > > > > > > > > > > So fail if needs_update? > > > > > > > > > > > > > > > > Kent. > > > > > > > > > > > > > > I'd say: do an implicit update before setting config. > > > > > > > > > > > > > > > > > > > So gpiod_line_update if needs_update, and fail if that fails? > > > > > > > > > > > > Kent. > > > > > > > > > > Without the if - needs_update is only set if an implicit update fails > > > > > in line_maybe_update(). But in this case we need to be sure, so do it > > > > > unconditionally. > > > > > > > > > > > > > Given that line_maybe_update is called at the end of request creation, and > > > > whenever set_config is called, how can line->direction be inconsistent > > > > with the kernel state - as long as needs_update is false? > > > > > > > > > > I don't think we should call line_maybe_update() on set_config() - in > > > this case we should call gpiod_line_update() and fail in set_config() > > > if it fails. > > > > > > I hope that's clearer. > > > > > > > Not really. I was already shaky on the needs_update and I'm getting more > > confused about the overall needs_update handling policy by the minute. > > > > Yeah it's not optimal. If you have better ideas on how to handle the > fact that the kernel can't really notify us about the changes in > line's flags introduced by other processes - I'll be more than glad to > give them a try. At some point I was thinking about another ioctl() > that - for a requested line - would return a file descriptor which > would emit events when a line changes - for instance, it's requested > by someone else or its direction is changed etc. > I didn't realise it was possible for a requested line's flags to be changed by other processes. Quite the opposite - I thought that was one of the reasons for GPIOD was to allow the userspace to prevent other from processes messing with requested lines. Kent. > I then thought that nobody is requesting this yet and so it may be overkill. > > Bart > > > Perhaps it will be more productive to go to the code. > > I'll send out what I have as v2 and we can go from there. > > > > Cheers, > > Kent.