Date: Fri, 7 Jun 2019 10:23:06 -0700 From: Nicola Mingotti <nmingotti@gmail.com> To: Ian Lepore <ian@freebsd.org>, Sergey Manucharian <sm@ara-ler.com> Cc: nmingott@gmail.com, freebsd-arm@freebsd.org Subject: Re: How to set PWM tunable name to ehrpwm.1 ? Message-ID: <f1e1609d-beba-1d49-faf0-ba470c00a773@gmail.com> In-Reply-To: <ee540fb38eca660a722f561fc91b660560133ed5.camel@freebsd.org> References: <68790975-a5a5-2138-ca89-117878d6cf2d@gmail.com> <20190606220639.GE13546@eldorado> <8126fa4ae0ca650ca12f28dd538e6e8c4e81b432.camel@freebsd.org> <2852b9da-e647-69a7-3218-88cfa500eadc@gmail.com> <ee540fb38eca660a722f561fc91b660560133ed5.camel@freebsd.org>
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On 6/7/19 7:58 AM, Ian Lepore wrote: > On Fri, 2019-06-07 at 02:08 -0700, Nicola Mingotti wrote: >> On 6/6/19 3:40 PM, Ian Lepore wrote: >>> On Thu, 2019-06-06 at 16:06 -0600, Sergey Manucharian wrote: >>>> Excerpts from Nicola Mingotti's message from Thu 06-Jun-19 12:33: >>>>> In my BeagleBone Black, FreeBSD-12 RELEASE, i created two >>>>> overlays, >>>>> pwm.dtso and pwm1.dtso. They enable the PWM pins p9.21, p9.22 >>>>> and >>>>> respectively p9.14, p9.16. DTSO files are below. >>>>> >>>>> If I load both the DTBO at boot I see >>>>> correctly|ehrpwm.0|and|ehrpwm.1|, >>>>> associated to the correct pins. But, if i remove the >>>>> overlay|pwm.dtbo|then i seen only|ehrpwm.0|in|sysctl -a|, which >>>>> is >>>>> not >>>>> what i want, i would like to see the name|ehrpwm.1|. >>>>> >>>>> This is important because i must be 100% sure a certain pin >>>>> corresponds >>>>> the a certain tunable.This must be true even if i remove non >>>>> relevant >>>>> overlays in the future. I guess there must be some parameter in >>>>> the >>>>> DTSO >>>>> which i don't know, i hope you can give me some directions >>>>> about >>>>> that. >>>> It is not related to your DTBO's. That's how everything works (at >>>> least >>>> by default). You will see the same naming issue with serial >>>> ports, >>>> for >>>> example. And not just in BBB. >>>> >>>> E.g. when I have enabled uart0 and uart2 they are named ttyu0 and >>>> ttyu1, >>>> if I have only uart2, it becomes ttyu0. >>>> >>>> It's easier if there is a device node in /dev, so you can create >>>> a >>>> symlink >>>> with a fixed name (I have a script called by devd for my multiple >>>> serial >>>> ports). However, that's not the case with PWM... >>>> >>>> Maybe there is an option to use persistent names for devices that >>>> somebody >>>> can point to. >>>> >>> Nope, there's no magic thing you're missing that fixes >>> this. Devices >>> get named-and-numbered based on the order of instantiation. >>> >>> Since what really matters here is the sysctl names, we could change >>> the >>> driver to install the sysctl nodes using the fdt device node names >>> instead of the freebsd newbus device names. Hmm, actually, since >>> people may be relying on the current names, I guess what we'd have >>> to >>> do is install another set of sysctl names based on fdt name >>> (basically >>> a set of alias names). >>> >>> -- Ian >>> >> I see, I agree changing the default naming scheme may damage who is >> relaying on it. It is not a good idea. Maybe it could be implemented >> in >> release 13. >> >> To Sergey. I used devd in the past, it works well. But i would >> prefer >> not to use it in this case, even if I had a /dev/xyz file available. >> The >> reason is that the /dev/xyz file would appear before the the devd >> daemon >> starts up (i guess), so the case would not stricly be covered by >> what >> the devd man page says devd should do. >> $> man devd >> => " ... Whenever a device is added to or removed from the device >> tree ... " >> >> To Ian. The idea of the alias seems good. I don't know at all what >> you >> can manage to do at the kernel level with the tunables. I imagine >> something like |dev.alias.am335x_ehrpwm.1| which actually refers to >>> EHRPWM1| not the second |ehrpwm| that got plugged into the system >>> via >> overlay. >> >> Thank you for your answers >> >> > The dev.* hierarchy is managed by newbus; what I was picturing was > something like hw.ehrpwm1.freq and so on, settable as either tunable or > sysctl. But it turns out ehrpwm1 is just a label in the dts, not > accessible at runtime. The actual node name is just 'pwm' and really, > nothing prevents upstream from changing that name on a whim next time > we import new dts files. (And linux sure seems to have a lot of > arbitrary whims when it comes to changing dts.) > > Since an overlay is required to use this stuff anyway, I'm now thinking > a custom property in the overlay that names the sysctl nodes might be a > good option. So you'd add a property like: > > &ehrpwm0 { > status = "okay"; > pinctrl-names = "default"; > pinctrl-0 = <&ehrpwm0_AB_pins>; > freebsd,sysctl = "backlight"; > }; > > And that would make it install names like hw.backlight.freq and > hw.backlight.period and so on. If you don't add that property, it just > installs the names it uses now (dev.ehrpwm.*) for compatibility. > > -- Ian > > Ian, this |freebsd,sysctl = "foobar"| to me sounds as a very good solution. In this way I could name the tunable with the "hardware name" or also with the functional name, as "pwm-motor-front-left". This would improve the readability of underlying software structure. That would be beautiful. n.
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