On Tue, Sep 28, 2021 at 10:54:26PM -0500, Samuel Holland wrote: > Hi Maxime, > > Thanks for your reply. > > On 9/28/21 4:06 AM, Maxime Ripard wrote: > > On Tue, Sep 28, 2021 at 02:46:39AM -0500, Samuel Holland wrote: > >> On 9/9/21 3:45 AM, Maxime Ripard wrote: > >>> On Fri, Sep 03, 2021 at 10:21:13AM -0500, Samuel Holland wrote: > >>>> On 9/3/21 9:50 AM, Maxime Ripard wrote: > >>>>> And since we can register all those clocks at device probe time, we > >>>>> don't really need to split the driver in two (and especially in two > >>>>> different places). The only obstacle to this after your previous series > >>>>> is that we don't have of_sunxi_ccu_probe / devm_sunxi_ccu_probe > >>>>> functions public, but that can easily be fixed by moving their > >>>>> definition to include/linux/clk/sunxi-ng.h > >>>> > >>>> Where are you thinking the clock definitions would go? We don't export > >>>> any of those structures (ccu_mux, ccu_common) or macros > >>>> (SUNXI_CCU_GATE_DATA) in a public header either. > >>> > >>> Ah, right... > >>> > >>>> Would you want to export those? That seems like a lot of churn. Or would > >>>> we put the CCU descriptions in drivers/clk/sunxi-ng and export a > >>>> function that the RTC driver can call? (Or some other idea?) > >>> > >>> I guess we could export it. There's some fairly big headers in > >>> include/linux/clk already (tegra and ti), it's not uAPI and we do have > >>> reasons to do so, so I guess it's fine. > >>> > >>> I'd like to avoid having two drivers for the same device if possible, > >>> especially in two separate places. This creates some confusion since the > >>> general expectation is that there's only one driver per device. There's > >>> also the fact that this could lead to subtle bugs since the probe order > >>> is the link order (or module loading). > >> > >> I don't think there can be two "struct device"s for a single OF node. > > > > That's not what I meant, there's indeed a single of_node for a single > > struct device. If we dig a bit into the core framework, the most likely > > scenario is that we would register both the RTC and clock driver at > > module_init, and with the device already created with its of_node set > > during the initial DT parsing. > > > > We register our platform driver using module_platform_driver, which > > expands to calling driver_register() at module_init(), setting the > > driver bus to the platform_bus in the process (in > > __platform_driver_register()). > > > > After some sanity check, driver_register() calls bus_add_driver(), which > > will call driver_attach() if drivers_autoprobe is set (which is the > > default, set into bus_register()). > > > > driver_attach() will, for each device on the platform bus, call > > __driver_attach(). If there's a match between that device and our driver > > (which is evaluated by platform_match() in our case), we'll call our > > driver probe with that device through driver_probe_device(), > > __driver_probe_device() and finally really_probe(). > > > > However, at no point in time there's any check about whether that device > > has already been bound to a driver, nor does it create a new device for > > each driver. > > I would expect this to hit the: > > if (dev->driver) > return -EBUSY; > > in __driver_probe_device(), or fail the "if (!dev->driver)" check in > __driver_attach() for the async case, once the first driver is bound. Hmmm, it might. I know we "leveraged" this some time ago for another platform, but it might not be working anymore indeed. > > So this means that, if you have two drivers that match the > > same device (like our clock and RTC drivers), you'll have both probe > > being called with the same device, and the probe order will be defined > > by the link order. Worse, they would share the same driver_data, with > > each driver not being aware of the other. This is incredibly fragile, > > and hard to notice since it goes against the usual expectations. > > > >> So if the CCU part is in drivers/clk/sunxi-ng, the CCU "probe" > >> function would have to be called from the RTC driver. > > > > No, it would be called by the core directly if there's a compatible to > > match. > > > >> Since there has to be cooperation anyway, I don't think there would be > >> any ordering problems. > > > > My initial point was that, with a direct function call, it's both > > deterministic and obvious. > > I believe I did what you are suggesting for v2. From patch 7: > > --- a/drivers/rtc/rtc-sun6i.c > +++ b/drivers/rtc/rtc-sun6i.c > @@ -683,6 +684,10 @@ static int sun6i_rtc_probe(struct platform_device > *pdev) > chip->base = devm_platform_ioremap_resource(pdev, 0); > if (IS_ERR(chip->base)) > return PTR_ERR(chip->base); > + > + ret = sun6i_rtc_ccu_probe(&pdev->dev, chip->base); > + if (ret) > + return ret; > } Ah, sorry, I entirely missed it. Yes, that totally fine by me then. I'd prefer to have the spinlock passed as an argument as well, but it can be done in a follow-up patch. > platform_set_drvdata(pdev, chip); > > >>> And synchronizing access to registers between those two drivers will be > >>> hard, while we could just share the same spin lock between the RTC and > >>> clock drivers if they are instanciated in the same place. > >> > >> While the RTC driver currently shares a spinlock between the clock part > >> and the RTC part, there isn't actually any overlap in register usage > >> between the two. So there doesn't need to be any synchronization. > > > > I know, but this was more of a social problem than a technical one. Each > > contributor and reviewer in the future will have to know or remember > > that it's there, and make sure that it's still the case after any change > > they make or review. > > > > This is again a fairly fragile assumption. > > Yeah, I agree that having a lock that is only sometimes safe to use with > certain registers is quite fragile. > > Would splitting the spinlock in rtc-sun6i.c into "losc_lock" (for the > clock provider) and "alarm_lock" (for the RTC driver) make this > distinction clear enough? > > Eventually, I want to split up the struct between the clock provider and > RTC driver so it's clear which members belong to whom, and there's no > ugly global pointer use. Maybe I should do this first? Yeah, it sounds like a good plan Thanks! Maxime
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