> -----Original Message----- > From: Linus Torvalds <[email protected]> > Sent: Saturday, August 29, 2020 4:20 PM > To: Guenter Roeck <[email protected]> > Cc: Luc Van Oostenryck <[email protected]>; Herbert Xu > <[email protected]>; Andrew Morton <akpm@linux- > foundation.org>; Joerg Roedel <[email protected]>; Leo Li > <[email protected]>; Zhang Wei <[email protected]>; Dan Williams > <[email protected]>; Vinod Koul <[email protected]>; linuxppc-dev > <[email protected]>; dma <[email protected]>; Linux > Kernel Mailing List <[email protected]> > Subject: Re: [PATCH] fsldma: fsl_ioread64*() do not need lower_32_bits() > > On Sat, Aug 29, 2020 at 1:40 PM Guenter Roeck <[email protected]> wrote: > > > > Except for > > > > CHECK: spaces preferred around that '+' (ctx:VxV) > > #29: FILE: drivers/dma/fsldma.h:223: > > + u32 val_lo = in_be32((u32 __iomem *)addr+1); > > Added spaces. > > > I don't see anything wrong with it either, so > > > > Reviewed-by: Guenter Roeck <[email protected]> > > > > Since I didn't see the real problem with the original code, I'd take > > that with a grain of salt, though. > > Well, honestly, the old code was so confused that just making it build is > clearly already an improvement even if everything else were to be wrong. > > So I committed my "fix". If it turns out there's more wrong in there and > somebody tests it, we can fix it again. But now it hopefully compiles, at > least. > > My bet is that if that driver ever worked on ppc32, it will continue to work > whatever we do to that function. > > I _think_ the old code happened to - completely by mistake - get the value > right for the case of "little endian access, with dma_addr_t being 32-bit". > Because then it would still read the upper bits wrong, but the cast to > dma_addr_t would then throw those bits away. And the lower bits would be > right. > > But for big-endian accesses or for ARCH_DMA_ADDR_T_64BIT it really looks > like it always returned a completely incorrect value. > > And again - the driver may have worked even with that completely incorrect > value, since the use of it seems to be very incidental. > > In either case ("it didn't work before" or "it worked because the value > doesn't really matter"), I don't think I could possibly have made things > worse. > > Famous last words.
Thanks for the patch. Acked-by: Li Yang <[email protected]> We are having periodical auto regression tests covering ppc32 platforms. But looks like it missed this issue. I will ask the test team to investigate on why the test cases are not sufficient. Regards, Leo
