From mboxrd@z Thu Jan 1 00:00:00 1970 From: Boris Brezillon Subject: Re: [PATCH v6 2/2] mfd: atmel-flexcom: add a driver for Atmel Flexible Serial Communication Unit Date: Thu, 23 Jul 2015 14:50:07 +0200 Message-ID: <20150723145007.099d01c2@bbrezillon> References: <7639e02fc2b16dc20b19fbe3bbbb986b0f3b9887.1437558598.git.cyrille.pitchen@atmel.com> <20150723073217.GT3061@x1> <20150723100101.7290242b@bbrezillon> <20150723091311.GX3061@x1> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20150723091311.GX3061@x1> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Lee Jones Cc: Cyrille Pitchen , nicolas.ferre-AIFe0yeh4nAAvxtiuMwx3w@public.gmane.org, alexandre.belloni-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org, sameo-VuQAYsv1563Yd54FQh9/CA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, pawel.moll-5wv7dgnIgG8@public.gmane.org, mark.rutland-5wv7dgnIgG8@public.gmane.org, ijc+devicetree-KcIKpvwj1kUDXYZnReoRVg@public.gmane.org, galak-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: devicetree@vger.kernel.org On Thu, 23 Jul 2015 10:13:11 +0100 Lee Jones wrote: > On Thu, 23 Jul 2015, Boris Brezillon wrote: > > > Hi Lee, > > > > On Thu, 23 Jul 2015 08:32:17 +0100 > > Lee Jones wrote: > > > > > On Wed, 22 Jul 2015, Cyrille Pitchen wrote: > > > > + for_each_child_of_node(np, child) { > > > > + const char *compatible; > > > > + int cplen; > > > > + > > > > + if (!of_device_is_available(child)) > > > > + continue; > > > > + > > > > + compatible = of_get_property(child, "compatible", &cplen); > > > > + if (!compatible || strlen(compatible) > cplen) > > > > + continue; > > > > + > > > > + if (strstr(compatible, "-usart")) { > > > > + opmode = FLEX_MR_OPMODE_USART; > > > > + break; > > > > + } > > > > + > > > > + if (strstr(compatible, "-spi")) { > > > > + opmode = FLEX_MR_OPMODE_SPI; > > > > + break; > > > > + } > > > > + > > > > + if (strstr(compatible, "-i2c")) { > > > > + opmode = FLEX_MR_OPMODE_TWI; > > > > + break; > > > > + } > > > > + } > > > > > > From what I understand Flexcom is a wrapper which can sit above any > > > number of SPI, I2C and/or UART devices. Devices which you don't > > > really have any control over (source code wise). So wouldn't it be > > > better to match on the details you do have control over i.e. the node > > > name, rather than the compatible string? > > > > > > I would personally match on of_find_node_by_name() to future-proof > > > your implementation. > > > > Actually, I think using compatible strings is more future-proof than > > using the node names, because nothing in the DT bindings doc enforce the > > node name, and usually what we use to attach a node to a specific > > driver is the compatible string (this one is specified in the bindings > > doc). > > I know what you're saying, but what if someone uses the Flexcom driver > to wrap a different type of SPI driver where (for instance) the > compatible string used is "-". Then we'd have to keep > adding more lines here to accommodate. > > Whereas if we used the child node name which only pertains to _this_ > driver, we would then have full control and know that (unless it > Flexcom is used for a completely different type of serial controller) > we wouldn't have to keep expanding the code to accommodate. You're right about the complexity implied by the compat string maintenance, but I still think using node names to detect the mode is a bad idea. Let's take another example making both solution unsuitable: what if the flexcom-v2 exposes 2 devices of the same type, they will both have the same name and the same compatible string, and we'll have no way to detect the appropriate mode. That's why I think none of our suggestion is future-proof. > > > Regarding the implementation itself, I would match the child node with > > an of_device_id table rather than trying to find a specific substring > > in the compatible string, but I think that's only a matter of taste. > > You mean duplicate each of the supported device's compatible strings > in this driver, then fetch the attributed of_match_device()->data > value? > Yes, and that's definitely not a good idea, but I think Cyrille has found a better approach (I'll let him explain). Best Regards, Boris -- Boris Brezillon, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html