12:59 a.m.
pon., 14 lut 2022 o 14:28 Andy Shevchenko
<andriy.shevchenko(a)linux.intel.com> napisał(a):
On Mon, Feb 14, 2022 at 01:27:35PM +0100, Jan Dąbroś wrote:
> pt., 11 lut 2022 o 22:24 kernel test robot <lkp(a)intel.com> napisał(a):
> > 159
> > 160 /* Helper to verify status returned by PSP */
> > 161 static int check_i2c_req_sts(struct psp_i2c_req *req)
> > 162 {
> > 163 int status;
> > 164
> > > 165 status = readl(&req->hdr.status);
>
> Actually the above error points to something hidden but important -
> for reading from command-response buffer, we shouldn't use __iomem
> specifier (nor readl() family of functions) since this is normal
> memory - however updated by PSP. Thus I will refactor this to use
> 'volatile u32 *' and reading status by de-referencing pointer.
Not sure volatile is a good idea. Perhaps READ_ONCE() is what you need.
Is this a system memory?
Yes, this is system memory.
Actually looking at asm-generic/rwonce.h:
#define __READ_ONCE(x) (*(const volatile __unqual_scalar_typeof(x) *)&(x))
it is more-less based on volatile, so that compiler will not be able
to (among others) optimize out such reads of memory which may be
changed outside of the scope of "program".
I believe that I will get the same outcome from using READ_ONCE and
explicit volatile, is the first way preferred in the kernel?
Best Regards,
Jan