On Fri, Mar 21, 2014 at 05:15:34PM +0530, Viresh Kumar wrote: > On 21 March 2014 16:34, Gautham R Shenoy <e...@linux.vnet.ibm.com> wrote: > > Heh! Well, that wasn't the reason why this was sent out as a separate > > patch, but never mind. Though I don't understand why it would be > > difficult to review the patch though. > > Because the initial driver wasn't complete earlier. There were 2-3 patches > after the first one which are changing what the first patch has added. > Nothing else :) > > >> > +static void powernv_read_cpu_freq(void *ret_freq) > >> > +{ > >> > + unsigned long pmspr_val; > >> > + s8 local_pstate_id; > >> > + int *cur_freq, freq, pstate_id; > >> > + > >> > + cur_freq = (int *)ret_freq; > >> > >> You don't need cur_freq variable at all.. > > > > I don't like it either. But the compiler complains without this hack > > :-( > > Why would the compiler warn for doing this?: > > *(int *)ret_freq = freq;
The compiler doesn't complain if I do this. > > >> > + pmspr_val = get_pmspr(SPRN_PMSR); > >> > + > >> > + /* The local pstate id corresponds bits 48..55 in the PMSR. > >> > + * Note: Watch out for the sign! */ > >> > + local_pstate_id = (pmspr_val >> 48) & 0xFF; > >> > + pstate_id = local_pstate_id; > >> > >> similarly local_pstate_id > > > > well, I am interested in the bits 48..55 of pmspr_val. That's the > > pstate_id which can be negative. So I'll like to keep > > local_pstate_id. > > Can you please explain at bit level how getting the value in a s8 > first and then into a s32 will help you here? Instead of getting it > directly into s32. Consider the case when pmspr = 0x00feffffffffffff; We are interested in extracting the value 'fe'. And ensure that when we store this value into an int, we get the sign extension right. So the following doesn't work: pstate_id = (pmspr_val >> 48) & 0xFFFFFFFF; Since we get pstate_id = 0x000000fe, which is not the same as 0xfffffffe. Of course, we could do the following, but I wasn't sure if two levels of type casting helped on the readability front. pstate_id = (int) ((s8)((pmspr_val >> 48) & 0xFF)); -- Thanks and Regards gautham. > _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev