Hi, On Fri, Jun 20, 2014 at 4:19 AM, amit daniel kachhap <amit.daniel@xxxxxxxxxxx> wrote: > On Fri, Jun 20, 2014 at 1:45 PM, Will Deacon <will.deacon@xxxxxxx> wrote: >> On Thu, Jun 19, 2014 at 05:40:49PM +0100, Tomasz Figa wrote: >>> On 19.06.2014 18:31, Doug Anderson wrote: >>> >>> My personal vote would be to submit a patch to change "cycles_t" to >>> >>> always be 32-bits. Given that 32-bits was fine for udelay() for ARM >>> >>> that seems sane and simple. If someone later comes up with a super >>> >>> compelling reason why we need 64-bit timers for udelay (really??) then >>> >>> they can later add all the complexity needed. >>> >> >>> >> Yes, this could work. I'm not sure what else cycles_t is used for, though. >>> > >>> > True, it is a bit questionable to change this since it's a type that's >>> > not obviously just for udelay(). Perhaps a better option would be to >>> > make a new typedef for the result of read_current_timer(). ...or just >>> > change it to return a u32? >>> > >>> >>> Sounds good to me, but let's hear other opinions. I'm adding Will and >>> Jonathan as they wrote the ARM delay timer code. >> >> I think cycles_t is only used for small interval calculations at the moment, >> but I remember Ted mentioning something about using it (or something >> similar) as a source of early entropy, in which case the more bits the >> better. >> > Will, > Thanks for the clarification that cycles_t is used for short > intervals. So it is safe to return lower 32 bit > counter for read_current_timer. As I looked at it more, I realized that we have two types in Linux. There's cycle_t and cycles_t. Whoa, confusing! I'd perhaps advocate a wholesale rename of cycles_t to avoid the confusion. I don't have a good name for it, though. cycle32_t? Or we could just use u32 for the function... :-/ > Tomasz, Doug, > As of now let me send a minimal implementation of this read delay > timer to fix the broken udelay for exynos platforms so that it goes to > upstream in rc releases. I will also prepare a fix for all > raw_readl/writel in mct to relaxed version to make it consistent. I'm reworking my 32-bit conversion patches right now and it's getting messy to intermingle this with yours. I'm going to pick up your patch and include it in my series. I hope that's OK. My plan is: 1. For 3.16 I think it's important to fix the udelay() problems and trying to rework cycle_t there doesn't seem like it makes sense. I'll just use Amit's original code that uses exynos_frc_read(). It might not be quite as optimal but it's good as a safe bugfix. 2. I'll post the cleanup patch moving away from the __raw_readl / __raw_writel 3. I'll post a patch moving to 32-bit, including moving Amit's code to 32-bit but with a compile time warning for now. I'll add a KConfig depends to keep it from compiling on ARM64. We can improve this once we change the delay timer to always request 32-bits. -Doug -- 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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