From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rob Herring Subject: Re: [PATCH linux-next v9 2/3] mfd: devicetree: add bindings for Atmel Flexcom Date: Wed, 9 Sep 2015 19:06:19 -0500 Message-ID: <55F0C97B.80404@kernel.org> References: <90fa2e0ded92567a29c996658153d833aaa5e411.1441118159.git.cyrille.pitchen@atmel.com> <55EF7209.8060407@kernel.org> <55F0540F.6000102@atmel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <55F0540F.6000102@atmel.com> Sender: linux-kernel-owner@vger.kernel.org To: Cyrille Pitchen , nicolas.ferre@atmel.com, boris.brezillon@free-electrons.com, alexandre.belloni@free-electrons.com, sameo@linux.intel.com, lee.jones@linaro.org Cc: 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 09/09/2015 10:45 AM, Cyrille Pitchen wrote: > Hi Rob, >=20 > Le 09/09/2015 01:40, Rob Herring a =E9crit : >> On 09/01/2015 09:46 AM, Cyrille Pitchen wrote: >>> This patch documents the DT bindings for the Atmel Flexcom which wi= ll be >>> introduced by sama5d2x SoCs. These bindings will be used by the act= ual >>> Flexcom driver to be sent in another patch. >>> >>> Signed-off-by: Cyrille Pitchen >>> Acked-by: Boris Brezillon >>> Acked-by: Alexandre Belloni >> >> A few comments, but in general looks fine. >> >>> --- >>> .../devicetree/bindings/mfd/atmel-flexcom.txt | 67 ++++++++++= ++++++++++++ >>> 1 file changed, 67 insertions(+) >>> create mode 100644 Documentation/devicetree/bindings/mfd/atmel-fle= xcom.txt >>> >>> diff --git a/Documentation/devicetree/bindings/mfd/atmel-flexcom.tx= t b/Documentation/devicetree/bindings/mfd/atmel-flexcom.txt >>> new file mode 100644 >>> index 000000000000..fc3511e41542 >>> --- /dev/null >>> +++ b/Documentation/devicetree/bindings/mfd/atmel-flexcom.txt >>> @@ -0,0 +1,67 @@ >>> +* Device tree bindings for Atmel Flexcom (Flexible Serial Communic= ation Unit) >>> + >>> +The Atmel Flexcom is just a wrapper which embeds a SPI controller,= an I2C >>> +controller and an USART. Only one function can be used at a time a= nd is chosen >>> +at boot time according to the device tree. >> >> Doesn't the board design choose (unless pins go to a header)? >> >=20 > The function may be chosen once for all by the board design but if we= take the > sama5d2 xplained board as an example, most Flexcoms output their pins= to > headers. >=20 >>> + >>> +Required properties: >>> +- compatible: Should be "atmel,sama5d2-flexcom" >>> +- reg: Should be the offset/length value for Flexcom dedicated >>> + I/O registers (without USART, TWI or SPI registers). >>> +- clocks: Should be the Flexcom peripheral clock from PMC. >>> +- #address-cells: Should be <1> >>> +- #size-cells: Should be <1> >>> +- ranges: Should be one range for the full I/O register region >>> + (including USART, TWI and SPI registers). >>> +- atmel,flexcom-mode: Should be one of the 3 following macros as d= efined in >>> + include/dt-bindings/mfd/atmel-flexcom.h: >>> + - ATMEL_FLEXCOM_MODE_USART for USART >>> + - ATMEL_FLEXCOM_MODE_SPI for SPI >>> + - ATMEL_FLEXCOM_MODE_TWI for I2C >>> + >>> +Required child: >>> +a single child device of type matching the "atmel,flexcom-mode" pr= operty. >> >> Okay, but why not allow all children and use "status"? >> >=20 > That is exactly what was proposed in v6 of this series: allow more th= an one > child so possibly all children but only one "available" child (status= =3D=20 > "okay"). >=20 > The Flexocm driver still needs to find out the type of device of this > available child to know which function is to be enabled (USART, I2C o= r SPI). > So the "compatible" attribute was parsed using strstr() to search on = of the > patterns "usart", "spi" or "i2c". >=20 > However the use of strstr() was discussed to know whether the driver = should > looks for a partial or an exact match of the "compatible" string. > An exact match would require to keep the Flexcom driver synchonized w= ith the > 3 other drivers every time one of them introduces a new compatibility= string, > which whould have made every driver more difficult to maintain by cre= ating a > useless dependency. > So this implementation relying on the "compatible" attribute was aban= doned. >=20 > To sum up, no other reliable (and simple) means to guess/extact the d= evice > type from its DT node was found so we got back to the "atmel,flexcom-= mode" > property. I wasn't thinking removing this property. If the mode is configured by the bootloader, then you want to make updates to the configuration as simple as possible. Updating atmel,flexcom-mode and status for the children would be much more simple than creating the whole child node. If that's not a valid usecase, then never mind. Rob