From mboxrd@z Thu Jan 1 00:00:00 1970 From: Cyrille Pitchen Subject: Re: [PATCH linux-next v9 2/3] mfd: devicetree: add bindings for Atmel Flexcom Date: Mon, 21 Sep 2015 14:15:54 +0200 Message-ID: <55FFF4FA.6050100@atmel.com> References: <90fa2e0ded92567a29c996658153d833aaa5e411.1441118159.git.cyrille.pitchen@atmel.com> <55EF7209.8060407@kernel.org> <55F0540F.6000102@atmel.com> <55F0C97B.80404@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <55F0C97B.80404-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Rob Herring , nicolas.ferre-AIFe0yeh4nAAvxtiuMwx3w@public.gmane.org, boris.brezillon-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org, alexandre.belloni-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org, sameo-VuQAYsv1563Yd54FQh9/CA@public.gmane.org, lee.jones-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org Cc: 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 Hi Rob, Le 10/09/2015 02:06, Rob Herring a =E9crit : > On 09/09/2015 10:45 AM, Cyrille Pitchen wrote: >> Hi Rob, >> >> 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 w= ill be >>>> introduced by sama5d2x SoCs. These bindings will be used by the ac= tual >>>> 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-fl= excom.txt >>>> >>>> diff --git a/Documentation/devicetree/bindings/mfd/atmel-flexcom.t= xt 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 Communi= cation 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 = and is chosen >>>> +at boot time according to the device tree. >>> >>> Doesn't the board design choose (unless pins go to a header)? >>> >> >> The function may be chosen once for all by the board design but if w= e take the >> sama5d2 xplained board as an example, most Flexcoms output their pin= s to >> headers. >> >>>> + >>>> +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 = defined 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" p= roperty. >>> >>> Okay, but why not allow all children and use "status"? >>> >> >> That is exactly what was proposed in v6 of this series: allow more t= han one >> child so possibly all children but only one "available" child (statu= s =3D=20 >> "okay"). >> >> The Flexocm driver still needs to find out the type of device of thi= s >> available child to know which function is to be enabled (USART, I2C = or SPI). >> So the "compatible" attribute was parsed using strstr() to search on= of the >> patterns "usart", "spi" or "i2c". >> >> 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 = with the >> 3 other drivers every time one of them introduces a new compatibilit= y string, >> which whould have made every driver more difficult to maintain by cr= eating a >> useless dependency. >> So this implementation relying on the "compatible" attribute was aba= ndoned. >> >> To sum up, no other reliable (and simple) means to guess/extact the = device >> type from its DT node was found so we got back to the "atmel,flexcom= -mode" >> property. >=20 > I wasn't thinking removing this property. If the mode is configured b= y > 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= =2E > If that's not a valid usecase, then never mind. >=20 > Rob >=20 The Flexcom driver calls of_platform_populate(), so yes it's allowed an= d supported to put the 3 children in the DT as long as only one is availa= ble. Should I update the documentation to deal with optional children or lea= ve it as it is? Best Regards, Cyrille -- To unsubscribe from this list: send the line "unsubscribe devicetree" i= n the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html