Hi, On 10/02/2014 04:16 PM, [email protected] wrote: > On Thu, Oct 2, 2014 at 10:08 AM, Hans de Goede <[email protected]> wrote: >> Hi, >> >> On 10/02/2014 03:40 PM, [email protected] wrote: >>> On Thu, Oct 2, 2014 at 9:33 AM, Hans de Goede <[email protected]> wrote: >>>> Hi, >>>> >>>> On 10/02/2014 03:27 PM, [email protected] wrote: >>>>> On Thu, Oct 2, 2014 at 9:14 AM, Hans de Goede <[email protected]> wrote: >>>>>> Hi, >>>>>> >>>>>> On 10/02/2014 02:56 PM, [email protected] wrote: >>>>>>> On Thu, Oct 2, 2014 at 8:39 AM, Hans de Goede <[email protected]> >>>>>>> wrote: >>>>>>>> Hi, >>>>>>>> >>>>>>>> On 10/02/2014 02:22 PM, [email protected] wrote: >>>>>>>>> On Thu, Oct 2, 2014 at 2:42 AM, Hans de Goede <[email protected]> >>>>>>>>> wrote: >>>>>>>>>> Hi, >>>>>>>>>> >>>>>>>>>> On 10/01/2014 08:12 PM, Stephen Warren wrote: >>>>>>>>>>> On 10/01/2014 11:54 AM, [email protected] wrote: >>>>>>>>>>>> On Wed, Oct 1, 2014 at 1:26 PM, Hans de Goede >>>>>>>>>>>> <[email protected]> wrote: >>>>>>>>>>> ... >>>>>>>>>>>>> We've been over all this again and again and again. >>>>>>>>>>>>> >>>>>>>>>>>>> AAAARRRRRGGGGGGGGGGGGGGGGGHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH! >>>>>>>>>>>>> >>>>>>>>>>>>> All solutions provided sofar are both tons more complicated, then >>>>>>>>>>>>> the >>>>>>>>>>>>> simple solution of simply having the simplefb dt node declare >>>>>>>>>>>>> which >>>>>>>>>>>>> clocks it needs. And to make things worse all of them sofar have >>>>>>>>>>>>> unresolved issues (due to their complexity mostly). >>>>>>>>>>>>> >>>>>>>>>>>>> With the clocks in the simplefb node, then all a real driver has >>>>>>>>>>>>> to do, >>>>>>>>>>>>> is claim those same clocks before unregistering the simplefb >>>>>>>>>>>>> driver, >>>>>>>>>>>>> and everything will just work. >>>>>>>>>>>>> >>>>>>>>>>>>> Yet we've been discussing this for months, all because of some >>>>>>>>>>>>> vague worries from Thierry, and *only* from Thierry that this will >>>>>>>>>>>>> make simplefb less generic / not abstract enough, while a simple >>>>>>>>>>>>> generic clocks property is about as generic as things come. >>>>>>>>>>> >>>>>>>>>>> Note: I haven't been following this thread, and really don't have >>>>>>>>>>> the time to get involved, but I did want to point out one thing: >>>>>>>>>>> >>>>>>>>>>> As I think I mentioned very early on in this thread, one of the big >>>>>>>>>>> concerns when simplefb was merged was that it would slowly grow and >>>>>>>>>>> become a monster. As such, a condition of merging it was that it >>>>>>>>>>> would not grow features like resource management at all. That means >>>>>>>>>>> no clock/regulator/... support. It's intended as a simple stop-gap >>>>>>>>>>> between early platform bringup and whenever a real driver exists >>>>>>>>>>> for the HW. If you need resource management, write a HW-specific >>>>>>>>>>> driver. The list archives presumably have a record of the >>>>>>>>>>> discussion, but I don't know the links off the top of my head. If >>>>>>>>>>> nobody >>>>>>>>>>> other than Thierry is objecting, presumably the people who >>>>>>>>>>> originally objected simply haven't noticed this patch/thread. I >>>>>>>>>>> suppose it's possible they changed their mind. >>>>>>>>>>> >>>>>>>>>>> BTW, there's no reason that the simplefb code couldn't be >>>>>>>>>>> refactored out into a support library that's used by both the >>>>>>>>>>> simplefb we currently have and any new HW-specific driver. It's >>>>>>>>>>> just that the simplefb binding and driver shouldn't grow. >>>>>>>>>> >>>>>>>>>> The whole reason why we want to use simplefb is not just to get >>>>>>>>>> things >>>>>>>>>> running until HW specific driver is in place, but also to have early >>>>>>>>>> console >>>>>>>>>> output (to help debugging boot problems on devices without a serial >>>>>>>>>> console), >>>>>>>>>> in a world where most video drivers are build as loadable modules, >>>>>>>>>> so we >>>>>>>>>> won't have video output until quite late into the boot process. >>>>>>>>> >>>>>>>>> You need both. >>>>>>>>> >>>>>>>>> 1) temporary early boot console -- this is nothing but an address in >>>>>>>>> RAM and the x/y layout. The character set from framebuffer is built >>>>>>>>> into the kernel. The parallel to this is early-printk and how it uses >>>>>>>>> the UARTs without interrupts. This console vaporizes late in the boot >>>>>>>>> process -- the same thing happens with the early printk UART driver. >>>>>>>>> EARLYPRINTK on the command line enables this. >>>>>>>>> >>>>>>>>> 2) a device specific driver -- this sits on initrd and it loaded as >>>>>>>>> soon as possible. The same thing happens with the real UART driver for >>>>>>>>> the console. CONSOLE= on the command line causes the transition. There >>>>>>>>> is an API in the kernel to do this transition, I believe it is called >>>>>>>>> set_console() but it's been a while. >>>>>>>> >>>>>>>> Eventually we need both, yes. But 1) should stay working until 2) >>>>>>>> loads, >>>>>>>> not until some phase of the bootup is completed, but simply until 2) >>>>>>>> loads. >>>>>>> >>>>>>> No, that is where you get into trouble. The device specific driver has >>>>>>> to go onto initrd where it can be loaded as early in the boot process >>>>>>> as possible. >>>>>> >>>>>> This is an argument in the "you cannot do that" / "your use case is not >>>>>> valid" >>>>>> category, IOW this is not a technical argument. You say I cannot do that >>>>>> I >>>>>> say I can, deadlock. >>>>> >>>>> It is certainly possible to extend an earlyframebuffer to be able to >>>>> run as a user space console. It is just going to turn into a >>>>> Frankenmonster driver with piles of device specific, special case code >>>>> in it. >>>> >>>> There is nothing hardware specific about a framebuffer needing some >>>> clocks to not be disabled. Tons of SoC's will have this. Which clocks, >>>> that is hardware specific, but the framebuffer driver does not need to >>>> worry about that, it just sees a clocks property with some random clocks >>>> in there, and that is as generic as it gets. >>>> >>>>> I think that device specific code belongs in a device specific driver >>>>> and earlyframebuffer should handoff to it as soon as possible. >>>>> >>>>>> >>>>>> I've already explained that we not only can do that (we already have >>>>>> working >>>>>> code proving that), but also that this is something which we absolutely >>>>>> need: >>>>>> >>>>>>>> One example why this is necessary is e.g. to debug things where the >>>>>>>> problem >>>>>>>> is that the right module is not included in the initrd. >>>>> >>>>> A generic earlyframebuffer would show this error. >>>> >>>> If it reserves the clocks it needs, yes. If it does not then the clocks >>>> will >>>> be disabled before the initrd starts, and the screen will be black from >>>> then >>> >>> I thought the clock/regulator clean up happened after initrd loading, >>> but maybe that is not the case. >>> >>> A cleaner solution would then be to modify the clock/regulator clean >>> up to happen after driver loading is finished from initrd. Deferring >>> until after that completes is a fixed limit, everything is sitting >>> there in RAM. I would not propose extending it until harddisk based >>> loading happens. >>> >>> So there are two ways to do this... >>> 1) modify things like earlyconsole to protect device specific resource >>> (I think this is a bad idea) >> >> Why is this a bad idea? If the bootloader tells us exactly which resources >> are needed, then earlyconsole can claim them, and release them on >> handover to the real display driver.
Jon, can you please answer this ? I really really want to know why people think this is such a bad idea. Understanding why people think this is a bad idea is necessary to be able to come up with an alternative solution. >> >>> 2) delay the clock/regulator cleanup until after there is a fixed >>> window for device specific drivers to load in. Loading from initrd is >>> a fixed window. >> >> As I already explained by example in another mail, this won't work: >> >> "delaying over the initrd is not helpful. Not having the real driver >> load for whatever reasons, is not necessarily a boot blocking event, >> and if it us just missing will not lead to any error messages. >> >> So the boot will continue normally with a black screen, and things are >> still impossible to debug." >> >> We've been down the whole delay till $random point in time thing in the >> past with storage enumeration, where you need to wait for say all members >> of a raid set to show up. The lesson learned from that is that you should >> not wait $random time / event, but wait for the actual storage device to >> show up. >> >> And this is just like that, we need to wait for the actual display driver >> to have loaded and taken over before "cleaning up" the clocks used by >> the display engine. >> >> I guess we could just delay all clock cleanup until then, not really >> pretty, and I still prefer to just list the clocks in the simplefb >> dtnode, but if this version would be acceptable to all involved, I can >> live with it. >> >> Mike, would a patch adding 2 calls like these to the clock core be >> acceptable ? : >> >> clk_block_disable_unused() >> clk_unblock_disable_unused() >> >> Where an earlyconsole driver can then call clk_block_disable_unused(), >> which will turn any calls to clk_disable_unused into a nop. > > Is there a way to use the existing eprobe_defer system to do this? No, that is not what it is intended for (at all). If we go this way 2 subsystem specific calls for this is the best way to deal with this. Regards, Hans -- You received this message because you are subscribed to the Google Groups "linux-sunxi" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
