From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lee Jones Subject: Re: [PATCH v6 2/2] mfd: atmel-flexcom: add a driver for Atmel Flexible Serial Communication Unit Date: Fri, 24 Jul 2015 11:16:20 +0100 Message-ID: <20150724101620.GE3436@x1> References: <7639e02fc2b16dc20b19fbe3bbbb986b0f3b9887.1437558598.git.cyrille.pitchen@atmel.com> <20150723073217.GT3061@x1> <20150723100101.7290242b@bbrezillon> <20150723091311.GX3061@x1> <20150723145007.099d01c2@bbrezillon> <55B1195F.4000104@atmel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: <55B1195F.4000104@atmel.com> Sender: linux-kernel-owner@vger.kernel.org To: Cyrille Pitchen Cc: Boris Brezillon , nicolas.ferre@atmel.com, alexandre.belloni@free-electrons.com, sameo@linux.intel.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, robh+dt@kernel.org, pawel.moll@arm.com, mark.rutland@arm.com, ijc+devicetree@hellion.org.uk, galak@codeaurora.org, devicetree@vger.kernel.org List-Id: devicetree@vger.kernel.org On Thu, 23 Jul 2015, Cyrille Pitchen wrote: > Hi all, >=20 > Le 23/07/2015 14:50, Boris Brezillon a =C3=A9crit : > > On Thu, 23 Jul 2015 10:13:11 +0100 > > Lee Jones wrote: > >=20 > >> 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 =3D of_get_property(child, "compatible", &cplen); > >>>>> + if (!compatible || strlen(compatible) > cplen) > >>>>> + continue; > >>>>> + > >>>>> + if (strstr(compatible, "-usart")) { > >>>>> + opmode =3D FLEX_MR_OPMODE_USART; > >>>>> + break; > >>>>> + } > >>>>> + > >>>>> + if (strstr(compatible, "-spi")) { > >>>>> + opmode =3D FLEX_MR_OPMODE_SPI; > >>>>> + break; > >>>>> + } > >>>>> + > >>>>> + if (strstr(compatible, "-i2c")) { > >>>>> + opmode =3D 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-pro= of > >>>> your implementation. > >>> > >>> Actually, I think using compatible strings is more future-proof t= han > >>> using the node names, because nothing in the DT bindings doc enfo= rce 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 bin= dings > >>> doc). > >> > >> I know what you're saying, but what if someone uses the Flexcom dr= iver > >> to wrap a different type of SPI driver where (for instance) the > >> compatible string used is "-". Then we'd have to k= eep > >> adding more lines here to accommodate. > >> > >> Whereas if we used the child node name which only pertains to _thi= s_ > >> driver, we would then have full control and know that (unless it > >> Flexcom is used for a completely different type of serial controll= er) > >> we wouldn't have to keep expanding the code to accommodate. > >=20 > > 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. > >=20 > > Let's take another example making both solution unsuitable: what if > > the flexcom-v2 exposes 2 devices of the same type, they will both h= ave > > 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 suggest= ion > > is future-proof. > >=20 > >> > >>> Regarding the implementation itself, I would match the child node= with > >>> an of_device_id table rather than trying to find a specific subst= ring > >>> in the compatible string, but I think that's only a matter of tas= te. > >> > >> You mean duplicate each of the supported device's compatible strin= gs > >> in this driver, then fetch the attributed of_match_device()->data > >> value? > >> > >=20 > > Yes, and that's definitely not a good idea, but I think Cyrille has > > found a better approach (I'll let him explain). >=20 > Indeed, what about taking advantage of the "ranges" property? >=20 > For the Flexcom: > #address-cells =3D <2>; > #size-cells =3D <1>; > ranges =3D <1 0 0xf8034200 0x200 /* opmode 1: USART */ > 2 0 0xf8034400 0x200 /* opmode 2: SPI */ > 3 0 0xf8034600 0x200>; /* opmode 3: I2C */ >=20 > Then for the single available child (for instance the SPI controller)= : > reg =3D <2 0 0x200>; >=20 > So the Operating Mode to be set into the Flexcom Mode Register is rea= d from > the very first u32 of the "reg" property of the child. >=20 > No need to introduce any new DT property and the mapping remains easy= to > maintain to follow hardware upgrades. When we do things like this we normally do: reg , ; reg-names "base", "mode"; Then use: platform_get_resource_byname() =2E... to fetch them. --=20 Lee Jones Linaro STMicroelectronics Landing Team Lead Linaro.org =E2=94=82 Open source software for ARM SoCs =46ollow Linaro: Facebook | Twitter | Blog