On 05.06.2014 21:22, Doug Anderson wrote: > Tomasz, > > On Thu, Jun 5, 2014 at 12:14 PM, Tomasz Figa <tomasz.figa@xxxxxxxxx> wrote: >> On 05.06.2014 20:48, Doug Anderson wrote: >>> Tomasz / Mike, >>> >>> On Fri, May 30, 2014 at 9:32 AM, Doug Anderson <dianders@xxxxxxxxxxxx> wrote: >>>> Right now if you've got earlyprintk enabled on exynos5420-peach-pit >>>> then you'll get a hang on boot. Here's why: >>>> >>>> 1. The i2c-s3c2410 driver will probe at subsys_initcall. It will >>>> enable its clock and disable it. This is the clock "i2c2". >>>> 2. The act of disabling "i2c2" will disable its parents. In this case >>>> the parent is "aclk66_peric". There are no other children of >>>> "aclk66_peric" officially enabled, so "aclk66_peric" will be turned >>>> off (despite being CLK_IGNORE_UNUSED, but that's by design). >>>> 3. The next time you try to earlyprintk you'll do so without the UART >>>> clock enabled. That's because the UART clocks are also children of >>>> "aclk66_peric". You'll hang. >>>> >>>> There's no good place to put a clock enable for earlyprintk, which is >>>> handled by a bunch of assembly code. The best we can do is to handle >>>> this in the clock driver. >>>> >>>> Signed-off-by: Doug Anderson <dianders@xxxxxxxxxxxx> >>>> Tested-by: Javier Martinez Canillas <javier.martinez@xxxxxxxxxxxxxxx> >>>> --- >>>> Changes in v2: >>>> - Use GATE_A and clk_get(). Save the clock for putting later. >>>> - Return 0 from exynos5420_clk_late_init(). >>>> >>>> drivers/clk/samsung/clk-exynos5420.c | 33 +++++++++++++++++++++++++++++++-- >>>> 1 file changed, 31 insertions(+), 2 deletions(-) >>> >>> Are there other changes you'd like me to make to this? It would be >>> really nice to get this in for 3.16 so the system doesn't just >>> mysteriously hang when you use earlyprintk. >> >> We can probably take this as an -rc fix, so it should be fine. >> >> However I still don't see the point of exporting this clock and >> polluting the global clkdev namespace. Even the diffstat looks better in v1. > > OK, I'm happy to go back to v1 with the addition of the "return 0". > > Mike: are you OK with that? > One more question that just came to my mind: Why it is just the aclk66_peri and not its children related to UARTs? Exynos5420 clock driver still needs a little clean-up, so I'm okay with any fix for now and changing this later if needed, but is this gate clock for ACLK66_PERIC even needed? It seems to be marked with CLK_IGNORE_UNUSED which suggests that it is not needed in this driver at all, along with other similar clocks. AFAIK for power management purposes our fine-grained approach is fine and we shouldn't need to use the big gates. Best regards, Tomasz -- To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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