Hello Krzysztof, On 10/22/2015 03:43 AM, Krzysztof Kozlowski wrote: > On 22.10.2015 10:20, Javier Martinez Canillas wrote:> Hello Krzysztof, >> >> Thanks for your feedback. >> >> On 10/22/2015 02:36 AM, Krzysztof Kozlowski wrote: >>> On 22.10.2015 00:15, Javier Martinez Canillas wrote: >>>> The pwrseq_emmc driver does a eMMC card reset before a system reboot to >>>> allow broken or limited ROM boot-loaders (that don't have an eMMC reset >>>> logic) to be able to read the second stage from the eMMC. >>>> >>>> But this has to be called before a system reboot handler and while most >>>> of them use the priority 128, there are other restart handlers (such as >>>> the syscon-reboot one) that use a higher priority. So, use the highest >>>> priority to make sure that the eMMC hw is reset before a system reboot. >>>> >>>> Signed-off-by: Javier Martinez Canillas <javier@xxxxxxxxxxxxxxx> >>>> Tested-by: Markus Reichl <m.reichl@xxxxxxxxxxxxx> >>>> Tested-by: Anand Moon <linux.amoon@xxxxxxxxx> >>>> Reviewed-by: Alim Akhtar <alim.akhtar@xxxxxxxxxxx> >>>> >>>> --- >>>> Hello, >>>> >>>> This patch was needed since a recent series from Alim [0] added >>>> syscon reboot and poweroff support to Exynos SoCs and removed >>>> the reset handler in the Exynos Power Management Unit (PMU) code. >>>> >>>> But the PMU and syscon-reboot restart handler have a different >>>> priority so [0] breaks restart when eMMC is used on these boards. >>>> >>>> [0]: http://www.spinics.net/lists/arm-kernel/msg454396.html >>>> >>>> So this patch must be merged before [0] to avoid regressions. >>>> >>>> Best regards, >>>> Javier >>>> >>>> drivers/mmc/core/pwrseq_emmc.c | 6 +++--- >>>> 1 file changed, 3 insertions(+), 3 deletions(-) >>>> >>>> diff --git a/drivers/mmc/core/pwrseq_emmc.c b/drivers/mmc/core/pwrseq_emmc.c >>>> index 137c97fb7aa8..ad4f94ec7e8d 100644 >>>> --- a/drivers/mmc/core/pwrseq_emmc.c >>>> +++ b/drivers/mmc/core/pwrseq_emmc.c >>>> @@ -84,11 +84,11 @@ struct mmc_pwrseq *mmc_pwrseq_emmc_alloc(struct mmc_host *host, >>>> >>>> /* >>>> * register reset handler to ensure emmc reset also from >>>> - * emergency_reboot(), priority 129 schedules it just before >>>> - * system reboot >>>> + * emergency_reboot(), priority 255 is the highest priority >>>> + * so it will be executed before any system reboot handler. >>>> */ >>>> pwrseq->reset_nb.notifier_call = mmc_pwrseq_emmc_reset_nb; >>>> - pwrseq->reset_nb.priority = 129; >>>> + pwrseq->reset_nb.priority = 255; >>> >>> I see the problem which you are trying to solve but this may be tricker >>> then just kicking the number. Some of restart handlers are registered >>> with priority 192. I found few of such, like: at91_restart_nb, >>> zynq_slcr_restart_nb, rmobile_reset_nb (maybe more, I did not grep too >>> much). >>> >> >> Yes, the syscon-reboot restart handler also uses a priority 192 and that >> is why reboot with eMMC broke with Alim's patches since the PMU restart >> handler priority is 128. >> >>> I guess they chose the "192" priority on purpose. >>> >> >> I tried to understand what's the policy w.r.t priority numbering for >> restart handlers but only found this in the register_restart_handler >> kernel-doc [0]: >> >> /** >> * register_restart_handler - Register function to be called to reset >> * the system >> * @nb: Info about handler function to be called >> * @nb->priority: Handler priority. Handlers should follow the >> * following guidelines for setting priorities. >> * 0: Restart handler of last resort, >> * with limited restart capabilities >> * 128: Default restart handler; use if no other >> * restart handler is expected to be available, >> * and/or if restart functionality is >> * sufficient to restart the entire system >> * 255: Highest priority restart handler, will >> * preempt all other restart handlers >> >> So, reading that is not clear to me if only the values 0, 128 and 255 >> should be used or any value from 0-255. >> >> What's clear to me is that restart handlers to reset a specific hw block >> should be called before the restart handler that resets the whole system. >> >> The 192 seems to be used because there are other default restart handlers >> that are using a prio of 128. See for example the commit that changed the >> syscon-reboot prio from 128 to 192: >> >> b81180b3fd48 power: reset: adjust priority of simple syscon reboot driver > > But were are here not talking about syscon handler but the others. Now > you will be ahead of them. > Yes, I know that. My point was that the platforms were either not using the mmc-pwrseq-emmc or their system restart handler already had a lower priority but that is not true for at least rk3288-veyron as you said. >> >> So probably the 192 value was chosen because is in the middle of 128 and >> 255 but it seems to me a rather arbitrary value and I would prefer it to >> be documented in some place. >> >>> Effectively, now the emmc handler will be executed before their >>> handlers... is it an issue? Maybe some testing on these platforms is >>> necessary? >>> >> >> I don't think is an issue, the reason why I chose 255 is that it is >> a documented value in the kernel-doc and since is the highest prio, >> it makes sure the eMMC will be reset before any system restart handler. >> >> Also, the pwrseq_emmc driver is only used in platforms whose SoC ROM >> can either leave the eMMC in an unknown state so the kernel needs to >> hw reset the eMMC or does not have a reset logic so it can only read >> from an eMMC if is in a known state (i.e: after a reset from kernel). > > I think at least one platform may be affected because it used > mmc-pwrseq-emmc and gpio-restart. > > Look at rk3288-veyron.dtsi. > > Both of restart handlers had the priority of 129 which means that the > order of execution depends on probing sequence. Now you will make the > sequence strict - first mmc then gpio. > The behavior is going to change indeed in that board but no due probe order but because the gpio-restart handler dev node has priority = <200> which overrides the default 129 in the gpio-restart driver. So before $SUBJECT the eMMC restart handler was not executed but now it will be after this change. > You seems convinced that this is not a problem... I don't know. I would > prefer test this on affected platforms before risking to break them. > It's annoying if fix for one SoC breaks another. > Agreed. >> >> Since the current mmc_pwrseq_emmc_reset_nb notifier priority is 129, >> eMMC reset will not work if one of the platforms you mentioned needs >> this since the system restart handler with prio 192 will be executed >> before the eMMC one, leaving the eMMC in an unknown state on reboot. > > And now you will "fix this" by making eMMC working correctly. So let's > make it straight: > 1. Previously the eMMC could be left on these platforms in an unknown > state (because emmc handler was not executed). > 2. No one complained! Which could mean that in fact this was working fine... > 3. Now you will change it. > 4. Maybe someone will complain? > > Just test it (or get an ack/tested tag). That's all what is needed. > Yes, I never meant that the patch should be merged without testing... > >> And $SUBJECT should not cause any regressions for the platforms that >> are currently using the pwrseq_emmc, since the restart handler was >> already being called before the system restart handler so bumping >> the priority should not cause any effect. > > I found at least one platform where the sequence *might* change. There > could be more of them. > Agreed, I missed that rk3288-veyron is using a restart handler with higher priority and could be other boards too as you said. Let's see what is Marek's opinion since he added the pwrseq_emmc support and also what Ulf thinks about always doing a eMMC reset before reboot. I can't think how doing a eMMC card reset before reboot could affect a board but you are right that we don't know without testing. > Best regards, > Krzysztof > Best regards, -- Javier Martinez Canillas Open Source Group Samsung Research America -- 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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