From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jaya Kumar Subject: Re: [RFC 2.6.28 1/2] gpiolib: add set/get batch v4 Date: Mon, 19 Jan 2009 22:19:40 +0800 Message-ID: <45a44e480901190619i18749c75jaa2d4606da251921@mail.gmail.com> References: <12321862383405-git-send-email-jayakumar.lkml@gmail.com> <20090119100342.GA16400@pengutronix.de> Mime-Version: 1.0 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :date:message-id:subject:from:to:cc:content-type :content-transfer-encoding; bh=+JFljNVVjoq73Jx4Z8j4bgGLjMaXxw4ypxEzGf0Y/60=; b=MXNFioC/VoRDwTCvIxZLeosORjdkfMrbSNsk12m7uhaugngzJjgnbyxmUHMd2B98BF zwU8SYHt5q32QnrBEOwUpxYmNcOAi7YckA+d9baMsCSiBbjieHzJEU9a8d3SmHGOq6yJ X8N+1ZfWg0CGhgXIA0WQQ3GOdecsz29LVqO0s= In-Reply-To: <20090119100342.GA16400@pengutronix.de> Sender: linux-embedded-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="iso-8859-1" To: =?ISO-8859-1?Q?Uwe_Kleine=2DK=F6nig?= Cc: David Brownell , Eric Miao , Paulius Zaleckas , Geert Uytterhoeven , Sam Ravnborg , linux-arm-kernel@lists.arm.linux.org.uk, linux-fbdev-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org, linux-embedded@vger.kernel.org On Mon, Jan 19, 2009 at 6:03 PM, Uwe Kleine-K=F6nig wrote: > Hi Jaya, > > On Sat, Jan 17, 2009 at 05:57:17PM +0800, Jaya Kumar wrote: >> Hi friends, >> >> This is v4 of batch support for gpiolib. Thanks to David Brownell, E= ric Miao, >> David Hylands, Robin, Ben, Jamie and others for prior feedback. The = post for >> v3 summarized the previous discussion. Since then the changes I've m= ade are: >> - split the patches into generic and arch specific > IMHO this should be three patches: "gpiolib", "pxa" and "am300epd". > Well, ... Hi Uwe, Ok, will do. > >> +[OPTIONAL] Spinlock-Safe GPIO Batch access > Is it really spinlock safe in general? Or only if gpio_cansleep(gpio= ) > if false for each gpio to get or set? You are correct to raise this issue. It is only spinlock safe if chip->cansleep is false. Initially, I wasn't sure what to do. The original gpio set/get_value() just does; WARN_ON(extra_checks && chip->can_sleep); and it is documented as: " Spinlock-Safe GPIO access ------------------------- return zero. Also, using these calls for GPIOs that can't safely be ac= cessed without sleeping (see below) is an error. " I will change this in the batch code to return an error if can_sleep is detected on any involved gpio_chip. > >> +static int __generic_gpio_set_batch(struct gpio_chip *chip, unsigne= d offset, >> + u32 values, u32 bitmask, int w= idth) > IMHO a better name is __gpio_set_batch_generic (or > __gpiolib_set_batch_generic?), YMMV. Agreed. Will change. > >> +int __gpio_set_batch(unsigned gpio, u32 values, u32 bitmask, int bi= twidth) > Sometimes your width parameter is called bitwidth, sometimes width. = I'd > like to have that consistant. Ok, you're right. I'll fix this. > > While talking about this parameter. I don't really like it, because = you > can calculate it from bitmask. In an earlier mail you write: Agreed. > > bitwidth (needed to iterate and map to chip ngpios) could be > calculated from bitmask, but that involves iteratively countin= g > bits from the mask, so we would have to do 800*600 bit counts. > Unless, we do ugly things like cache the previous bitwidth/mas= k > and compare against the current caller arguments. Given that t= he > bitwidth would typically be a fixed value, I believe it is mor= e > intuitive for the caller to provide it, ... > > I think it's easier than that. bitwidth is just fls(bitmask) which > should be efficient enough not to bother the programmer. If bitmask = is > constant it's even the compiler that does the work here. > That is a good point. I agree that width is ugly in the main API. It is just fls(mask) and I now realize that this is an inline so you're right it would get taken care of by the compiler. fls is checked with __constant_fls first. Beauty! Thanks Uwe! I'll make these changes. Thanks, jaya