Messages in this thread | | | From | Adam Ford <> | Date | Tue, 2 Mar 2021 13:03:04 -0600 | Subject | Re: [PATCH V3] clk: imx: Fix reparenting of UARTs not associated with sdout |
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On Mon, Feb 15, 2021 at 7:06 AM Abel Vesa <abel.vesa@nxp.com> wrote: > > On 21-02-13 08:44:28, Adam Ford wrote: > > On Wed, Feb 3, 2021 at 3:22 PM Adam Ford <aford173@gmail.com> wrote: > > > > > > On Thu, Jan 21, 2021 at 4:24 AM Abel Vesa <abel.vesa@nxp.com> wrote: > > > > > > > > On 21-01-21 10:56:17, Sascha Hauer wrote: > > > > > On Wed, Jan 20, 2021 at 06:14:21PM +0200, Abel Vesa wrote: > > > > > > On 21-01-20 16:50:01, Sascha Hauer wrote: > > > > > > > On Wed, Jan 20, 2021 at 05:28:13PM +0200, Abel Vesa wrote: > > > > > > > > On 21-01-20 16:13:05, Sascha Hauer wrote: > > > > > > > > > Hi Abel, > > > > > > > > > > > > > > > > > > On Wed, Jan 20, 2021 at 04:44:54PM +0200, Abel Vesa wrote: > > > > > > > > > > On 21-01-18 08:00:43, Adam Ford wrote: > > > > > > > > > > > On Mon, Jan 18, 2021 at 6:52 AM Abel Vesa <abel.vesa@nxp.com> wrote: > > > > > > > > > > > > > > > > ... > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > TBH, I'm against the idea of having to call consumer API from a clock provider driver. > > > > > > > > > > > > I'm still investigating a way of moving the uart clock control calls in drivers/serial/imx, > > > > > > > > > > > > where they belong. > > > > > > > > > > > > > > > > > > > > > > That makes sense. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Just a thought. The uart clock used for console remains on from u-boot, > > > > > > > > > > so maybe it's enough to just add the CLK_IGNORE_UNUSED flag to all the > > > > > > > > > > uart root clocks and remove the prepare/enable calls for uart clocks > > > > > > > > > > for good. I don't really have a way to test it right now, but maybe > > > > > > > > > > you could give it a try. > > > > > > > > > > > > > > > > > > That would mean that UART clocks will never be disabled, regardless of > > > > > > > > > whether they are used for console or not. That doesn't sound very > > > > > > > > > appealing. > > > > > > > > > > > > > > > > AFAIK, the only uart clock that is enabled by u-boot is the one used for > > > > > > > > the console. Later on, when the serial driver probes, it will enable it itself. > > > > > > > > > > > > > > > > Unless I'm missing something, this is exactly what we need. > > > > > > > > > > > > > > It might enable it, but with CLK_IGNORE_UNUSED the clock won't be > > > > > > > disabled again when a port is closed after usage > > > > > > > > > > > > OK, tell me what I'm getting wrong in the following scenario: > > > > > > > > > > > > U-boot leaves the console uart clock enabled. All the other ones are disabled. > > > > > > > > > > > > Kernel i.MX clk driver registers the uart clocks with flag CLK_IGNORE_UNUSED. > > > > > > > > > > I was wrong at that point. I originally thought the kernel will never > > > > > disable these clocks, but in fact it only leaves them enabled during the > > > > > clk_disable_unused call. > > > > > > > > > > However, when CLK_IGNORE_UNUSED becomes relevant it's too late already. > > > > > I just chatted with Lucas and he told me what the original problem was > > > > > that his patch solved. > > > > > > > > > > The problem comes when an unrelated device and the earlycon UART have > > > > > the same parent clocks. The parent clock is enabled, but it's reference > > > > > count is zero. Now when the unrelated device probes and toggles its > > > > > clocks then the shared parent clock will be disabled due to the > > > > > reference count being zero. Next time earlycon prints a character the > > > > > system hangs because the UART gates are still enabled, but their parent > > > > > clocks no longer are. > > > > > > > > > > > > > Hmm, that is indeed a problem. That's why I think there should be some > > > > kind of NOCACHE flag for almost all the types of clocks. For example, > > > > in this case, it makes sense for the core to check the bit in the register > > > > and then disable the parent based on that instead of relying on the refcount. > > > > Anyway, that's something that needs to be added in the CCF. > > > > > > > > > Overall I think Lucas' patches are still valid and relevant and with > > > > > Adams patches we even no longer have to enable all UART clocks, but > > > > > only the ones which are actually needed. > > > > > > > > Yeah, for now, I think we can go with Adam's patches. But longterm, I would > > > > like to remove the special case of the uart clocks we have right now in all > > > > the i.MX clock drivers. > > > > I looked around at other serial drivers, and I found nothing like this > > function for enabling all UART clocks. There are generic functions > > for registering consoles, earlycon etc, and the serial driver fetches > > the per and igp clocks from the device tree, so I attempted to simply > > remove imx_register_uart_clocks(). I booted an i.MX8M Nano from a > > fully-powered off state, and my serial console came up just fine. > > Just because it works, doesn't mean it is safe. To put it simply, the > risk of some driver disabling a clock that is parent of the uart clock > would render the earlycon broken. > > > > > I checked the clk_summary, and the clock parents are set correctly and > > the respective clock rates appear to be correct (ie, the console is > > working at the desired baud rate, and Bluetooth is happy) > > > > Since I don't fully understand the serial driver and the clock > > dependencies, I don't want to just simply remove the function without > > discussing it, because I don't know the ramifications. However, when > > testing on the i.MX8M Nano, things look OK. > > I also tested suspend-resume and the console UART appears to return > > and the Bluetooth UART set to 4Mbps works just fine too. > > > > I'd like to post a V4 which just removes imx_register_uart_clocks and > > the corresponding calls to it. I don't know enough about the older > > 32-bit i.MX SoC's, but I have build-tested it, and I can generate a > > patch. Are there any objections and/or concerns? > > > > Please don't remove the imx_register_uart_clocks for now. As much as I > would like it gone, the way the earlycon could end up broken is > so ugly that it would make it a real pain to debug it later on.
I won't do a V4, but where do we go from here? I have a V3 that was waiting for reviews, but there were some concerns. We currently cannot re-parent the UART's on iMX8MM or iMX8MN. Should I resend V3, or are there fixes/changes requested to V3?
adam > > > adam > > > > > > > > > > Is the patch I submitted good enough for someone's acked-by or > > > reviewed-by, or are there changes I need to implement? > > > > > > adam > > > > > > > > > > > > > Sascha > > > > > > > > > > > > > > > -- > > > > > Pengutronix e.K. | | > > > > > Steuerwalder Str. 21 | https://eur01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.pengutronix.de%2F&data=04%7C01%7Cabel.vesa%40nxp.com%7C12862aeac2934a4a94f108d8d02de573%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C637488242849833051%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=fKDvWYJIU7hBROH6yDM9FYUCHJDK9wMjTeJDMxRff8o%3D&reserved=0 | > > > > > 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | > > > > > Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
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