On Mon, Dec 14, 2015 at 10:41 AM, Andrew F. Davis <afd@xxxxxx> wrote: > On 12/11/2015 03:48 PM, Linus Walleij wrote: >> >> On Fri, Dec 11, 2015 at 8:46 PM, Andrew F. Davis <afd@xxxxxx> wrote: >> >>> Add binding for generic parallel-in/serial-out shift register devices >>> used as GPIO. >>> >>> Signed-off-by: Andrew F. Davis <afd@xxxxxx> >> >> >>> +Generic Parallel-in/Serial-out Shift Register GPIO Driver >>> + >>> +This binding describes generic parallel-in/serial-out shift register >>> +devices that can be used for GPI (General Purpose Input). This includes >>> +SN74165 serial-out shift registers and the SN65HVS88x series of >>> +industrial serializers. >>> + >>> +Required properties: >>> + - compatible : Should be "pisosr-gpio". >> >> >> I think it should also define compatible strings on the "vendor,device" >> format apart from the generic compatible. Sooner or later we may need >> to differentiate them and then that comes in handy. >> > > Would it be better to wait until/if this issue arises? This driver > targets the generic features, as these parts are very generic and > have been produced by many companies since the 70s I'm not sure > if privileging any of them makes much sense. > > What I'm worried about looks to have happened with the gpio-74x164 > driver, this is kind of the companion device to mine (74164 / 74165) > and should work with any 74164 compatible shift register (possibly 100s > of versions of them), but the compatible string that was added is > "fairchild,74hc595", a relatively new device by a single manufacturer. > The problem this has is then that boards will use this compatible string > even if the parts are not actually the Fairchild version, just to get > the match, when they should be using a generic string. I agree the generic version is fine (or find who made the first part ;)). What "pisosr" is is not very obvious though. Having 74165 in the compatible would make it somewhat more obvious it is a standard logic part. >>> +Optional properties: >>> + - ngpios : Number of GPIO lines, default is 8. >> >> >> If you didn't do "pisosr-gpio" but instead "foo,sn74165", maybe you >> don't need to have this in the device tree but instead it can be >> determined from the compatible string? >> >> In that case do that. >> > > These devices can be daisy-chained together, so three 8bit registers > look exactly like one 24bit register. The only way to know this is > from the physical wiring of the board, not from the part number. Then you should say it must be multiple of 8 (or are there other lengths?). Rob -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
