On Mon, Dec 14, 2015 at 5:19 PM, Andrew F. Davis <afd@xxxxxx> wrote: > On 12/14/2015 04:36 PM, Rob Herring wrote: >> >> 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: [...] >>>>> + - 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. >> > > A quick search shows shift-registers being made from vacuum tubes for > the Colossus! Those might work with this driver if you could match the > voltage to an SPI bus... :) > > I agree about the name not being very good, but I'm not sure about > 74165 ether as it is also just a single part number. The idea was to > have a non-part number compatible string for any shift-register you > can hook to the SPI line. That way when we have boards with a sn65x882 > or something we wont have to call it a 74165. But I guess that's why > it's a "compatible:" string, and not "is-a:" string. If there are a couple then I think it is okay. If there are 10s then maybe not. Perhaps logic-pisosr or discrete-pisosr? >>>>> +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?). >> > > Some are 4bit, you can even just hook a single flip-flop to the SPI bus for > a single bit (or multiples) of input. One would hope you would just connect the CS signal directly to that input for 1-bit... I guess you could be out of GPIOs and only have a free output only CS signal. 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
