On Mon, Oct 7, 2024, at 14:40, Marius.Cristea@xxxxxxxxxxxxx wrote: > On Sun, 2024-09-29 at 21:16 +0000, David Laight wrote: >> [You don't often get email from david.laight@xxxxxxxxxx. Learn why >> this is important at https://aka.ms/LearnAboutSenderIdentification ;] >> >> EXTERNAL EMAIL: Do not click links or open attachments unless you >> know the content is safe >> >> From: marius.cristea@xxxxxxxxxxxxx >> > Sent: 27 September 2024 09:36 >> > >> > The PAC194X, IIO driver, is using some unaligned 56 bit registers. >> > Provide some helper accessors in preparation for the new driver. >> >> Someone please shoot the hardware engineer ;-) >> >> Do separate unaligned access of the first 4 bytes and last four >> bytes. >> It can't matter if the middle byte is accessed twice. >> >> Or, for reads read 8 bytes from 'p & ~1ul' and then fixup >> the value. >> > > Do you recommend me to drop this patch? > > I know that there are some "workarounds", but those didn't "looks" > nice. I was using that function locally and I got a suggestion from the > IIO subsystem maintainer to move it into the kernel in order for others > to used it. My feeling is that this is too specific to one driver, I don't expect it to be shared much. I also suspect that most 56-bit integers in data structures are actually always part of a naturally aligned 64-bit word. If that is the case here, the driver can probably better access it as a normal 64-bit number and mask out the upper 56 bits using the include/linux/bitfield.h helpers. Arnd
