Messages in this thread | | | Date | Tue, 26 Apr 2022 16:38:38 -0500 | From | Rob Herring <> | Subject | Re: [PATCH v5 04/11] clocksource/drivers: Add HPE GXP timer |
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On Tue, Apr 26, 2022 at 08:00:20AM +0200, Arnd Bergmann wrote: > On Mon, Apr 25, 2022 at 10:38 PM Linus Walleij <linus.walleij@linaro.org> wrote: > > On Fri, Apr 22, 2022 at 3:16 PM Arnd Bergmann <arnd@arndb.de> wrote: > > > On Thu, Apr 21, 2022 at 9:21 PM <nick.hawkins@hpe.com> wrote: > > > > > > > + > > > > +static struct platform_device gxp_watchdog_device = { > > > > + .name = "gxp-wdt", > > > > + .id = -1, > > > > +}; > > > > +/* > > > > + * This probe gets called after the timer is already up and running. This will create > > > > + * the watchdog device as a child since the registers are shared. > > > > + */ > > > > + > > > > +static int gxp_timer_probe(struct platform_device *pdev) > > > > +{ > > > > + struct device *dev = &pdev->dev; > > > > + > > > > + /* Pass the base address (counter) as platform data and nothing else */ > > > > + gxp_watchdog_device.dev.platform_data = local_gxp_timer->counter; > > > > + gxp_watchdog_device.dev.parent = dev; > > > > + return platform_device_register(&gxp_watchdog_device); > > > > +} > > > > > > I don't understand what this is about: the device should be created from > > > DT, not defined statically in the code. There are multiple ways of creating > > > a platform_device from a DT node, or you can allocate one here, but static > > > definitions are generally a mistake. > > > > > > I see that you copied this from the ixp4xx driver, so I think we should fix this > > > there as well. > > > > The ixp4xx driver looks like that because the register range used for > > the timer and the watchdog is combined, i.e. it is a single IP block: > > > > timer@c8005000 { > > compatible = "intel,ixp4xx-timer"; > > reg = <0xc8005000 0x100>; > > interrupts = <5 IRQ_TYPE_LEVEL_HIGH>; > > }; > > > > Device tree probing does not allow two devices to probe from the same > > DT node, so this was solved by letting the (less important) watchdog > > be spawn as a platform device from the timer. > > > > I don't know if double-probing for the same register range can be fixed, > > but I was assuming that the one-compatible-to-one-driver assumption > > was pretty hard-coded into the abstractions. Maybe it isn't? > > Having a child device is fine, my objection was about the way > the device is created from a 'static platform_device ...' definition > rather than having the device structure allocated at probe time. > > > Another way is of course to introduce an MFD. That becomes > > problematic in another way: MFD abstractions are supposed to > > be inbetween the resource and the devices it spawns, and with > > timers/clocksources this creates a horrible special-casing since the > > MFD bus (the parent may be providing e.g. an MMIO regmap) > > then need to be early-populated and searched by the timer core > > from TIMER_OF_DECLARE() early in boot. > > > > So this solution was the lesser evil that I could think about. > > There are multiple ways of doing this that we already discussed > in the thread. The easiest is probably to have a child node without > custom registers in the DT and then use the DT helpers to > populate the linux devices with the correct data.
I think that's what the wdt binding is doing, but I don't like that. Maybe it's not a child node, I can't tell.
Bindings should not be decided on the *current* driver split on one particular OS. This looks like 1 block, so 1 node. If that doesn't work well or easy for Linux, then we should fix Linux.
Rob
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