On Thu, Jan 24, 2013 at 11:37:30AM +0800, Feng Tang wrote:
> > I think hard numbers would be needed to show the rtc layer is
> > causing major issues for space constrained kernels, so this
> > trade-off could be properly prioritized. Having duplicate code paths
> > in standard kernels is wasteful as well.
> Another thing is currently the CONFIG_RTC_XXX is selectable option for
> kernel, if we push the read_persistent_clock() from kernel code down to
> rtc driver layer, then some of the CONFIG_RTC_XXX have to be always 'y'
All my space constrained embedded kernels (ARM, PPC) already need
CONFIG_RTC.. Configurations that can still access the RTC without
CONFIG_RTC seem to be very limited, the notable one is x86 - and I
don't think 14k is going to be a problem for any modern embedded x86
systems.
CONFIG_RTC_xx doesn't have to be forced to yes, it is like any other
driver, if you don't have/load a RTC driver then you don't get a RTC,
*shrug*
> > >IIRC, some EFI backed x86 system's read_persistent_clock() is
> > >implemented by EFI's runtime gettime service.
> > Interesting, does the rtc driver not support this?
>
> x86's read_persistent_clock() is actually implemented with
> retval = x86_platform.get_wallclock()
>
> And for x86_32 platform, the efi.c has code to set
> x86_platform.get_wallclock()
> to efi_get_time() which is efi's runtime service.
>
> I don't know the detail how it works, but I think it could co-exist with a
> rtc driver if there is.
Like the CMOS path, it completely duplicates the code in the EFI RTC
driver, so it should co-exist. The locking seems to be handled by the
EFI stuff:
unsigned long efi_get_time(void)
{
efi_status_t status;
efi_time_t eft;
efi_time_cap_t cap;
status = efi.get_time(&eft, &cap);
if (status != EFI_SUCCESS)
pr_err("Oops: efitime: can't read time!\n");
return mktime(eft.year, eft.month, eft.day, eft.hour,
eft.minute, eft.second);
}
vs:
static int efi_read_time(struct device *dev, struct rtc_time *tm)
{
efi_status_t status;
efi_time_t eft;
efi_time_cap_t cap;
status = efi.get_time(&eft, &cap);
if (status != EFI_SUCCESS) {
/* should never happen */
printk(KERN_ERR "efitime: can't read time\n");
return -EINVAL;
}
convert_from_efi_time(&eft, tm);
return rtc_valid_tm(tm);
}
Jason
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