Messages in this thread | | | From | "Li, Meng" <> | Subject | RE: [PATCH] mfd: altera-sysmgr: enable raw spinlock feature for preempt-rt kernel | Date | Tue, 16 Nov 2021 16:06:12 +0000 |
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> -----Original Message----- > From: Lee Jones <lee.jones@linaro.org> > Sent: Tuesday, November 16, 2021 11:39 PM > To: Li, Meng <Meng.Li@windriver.com> > Cc: Arnd Bergmann <arnd@arndb.de>; thor.thayer@linux.intel.com; Linux > Kernel Mailing List <linux-kernel@vger.kernel.org> > Subject: Re: [PATCH] mfd: altera-sysmgr: enable raw spinlock feature for > preempt-rt kernel > > [Please note: This e-mail is from an EXTERNAL e-mail address] > > On Tue, 16 Nov 2021, Li, Meng wrote: > > > > > > > > -----Original Message----- > > > From: Arnd Bergmann <arnd@arndb.de> > > > Sent: Tuesday, November 16, 2021 8:02 PM > > > To: Li, Meng <Meng.Li@windriver.com> > > > Cc: thor.thayer@linux.intel.com; Lee Jones <lee.jones@linaro.org>; > > > Arnd Bergmann <arnd@arndb.de>; Linux Kernel Mailing List <linux- > > > kernel@vger.kernel.org> > > > Subject: Re: [PATCH] mfd: altera-sysmgr: enable raw spinlock feature > > > for preempt-rt kernel > > > > > > [Please note: This e-mail is from an EXTERNAL e-mail address] > > > > > > On Tue, Nov 16, 2021 at 11:54 AM Meng Li <Meng.Li@windriver.com> > wrote: > > > > diff --git a/drivers/mfd/altera-sysmgr.c > > > > b/drivers/mfd/altera-sysmgr.c index 5d3715a28b28..27271cec5d53 > > > > 100644 > > > > --- a/drivers/mfd/altera-sysmgr.c > > > > +++ b/drivers/mfd/altera-sysmgr.c > > > > @@ -83,6 +83,9 @@ static struct regmap_config > > > > altr_sysmgr_regmap_cfg = > > > { > > > > .fast_io = true, > > > > .use_single_read = true, > > > > .use_single_write = true, > > > > +#ifdef CONFIG_PREEMPT_RT > > > > + .use_raw_spinlock = true, > > > > +#endif > > > > > > I think you should remove the #ifdef here: if PREEMPT_RT is > > > disabled, the flag has no effect because spinlock behaves the same > > > way as raw_spinlock. If anything else starts requiring the use of > > > raw spinlocks, then we probably want the flag to be set here as well. > > > > > > > Thanks for your suggestion, and I also agree with the spinlock action when > PREEMPT_RT is disabled. > > But please allow me to explain why I keep the "ifdef" > > 1. although I send this patch to mainline upstream, I only want to fix this > issue in RT kernel. > > Moreover, the commit 67021f25d952("regmap: teach regmap to use raw > spinlocks if requested in the config ") is also for RT kernel even if it doesn't > use "ifdef CONFIG_PREEMPT_RT" > > My ideal is that if this patch is merged into mainline, Linux-rt maintainer > will not spend extra effort to focus on this patch. After all, this fixing is more > related with driver. > > In addition, I found out there are other patches with "ifdef > CONFIG_PREEMPT_RT" merged by mainline, so I also send this patch to > mainline, not Linux-rt. > > > > 2. I check regmap.c code that is related with use_raw_spinlock. If > PREEMPT_RT is disabled and use_raw_spinlock is set as true, the else case > will not be entered any longer. > > In other words, in mainline standard kernel, if use_raw_spinlock is set as > true, raw spinlock will be used forever, and the code in else case will become > useless. > > I feel it is a little unreasonable. So, I keep the "ifdef" > > if ((bus && bus->fast_io) || > > config->fast_io) { > > if (config->use_raw_spinlock) { > > raw_spin_lock_init(&map->raw_spinlock); > > map->lock = regmap_lock_raw_spinlock; > > map->unlock = regmap_unlock_raw_spinlock; > > lockdep_set_class_and_name(&map->raw_spinlock, > > lock_key, lock_name); > > } else { > > spin_lock_init(&map->spinlock); > > map->lock = regmap_lock_spinlock; > > map->unlock = regmap_unlock_spinlock; > > lockdep_set_class_and_name(&map->spinlock, > > lock_key, lock_name); > > } > > } else { > > mutex_init(&map->mutex); > > map->lock = regmap_lock_mutex; > > map->unlock = regmap_unlock_mutex; > > map->can_sleep = true; > > lockdep_set_class_and_name(&map->mutex, > > lock_key, lock_name); > > } > > > > I dislike #ifery as a general rule. So with that in mind - if it's not required, I'd > prefer that it's removed. >
Ok! There is no real difference if remove the #ifery. I will check the standard kernel and then sent v3 RR.
Thanks, Limeng
> -- > Lee Jones [李琼斯] > Senior Technical Lead - Developer Services Linaro.org │ Open source > software for Arm SoCs Follow Linaro: Facebook | Twitter | Blog
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