On Tuesday 10 March 2015 08:43:22 Hans de Goede wrote: > On 09-03-15 22:50, Arnd Bergmann wrote: > > On Monday 09 March 2015 21:40:18 Hans de Goede wrote: > >> The generic fifo functions already use non wrapped accesses in various > >> cases through the iowrite#_rep functions, and all platforms which override > >> the default musb_read[b|w] / _write[b|w] functions also provide their own > >> fifo access functions, so we can safely drop the unnecessary indirection > >> from the fifo access functions. > >> > >> Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx> > >> > > > > The patch looks reasonably, but the description seem misleading. > > I believe the real reason why it's ok to use __raw_writew for the > > FIFO is that a FIFO by definition is using CPU endian access for > > copying byte streams from memory, which is unlike any other MMIO > > register that requires fixed-endian accessors. > > I'm not sure that that is the case here, this fifo allows reading > 4 bytes at a time using 32 bit word access, so endianness may come > into play. This patch is safe however since all existing users of > the generic fifo_read / write helpers which this patch touches, are > also using the generic musb_read[b|w] / _write[b|w] functions which > are just __raw_foo wrappers, so there is no functional change, which > is what the commit message tries to say. This probably means that the generic musb helpers are not safe to use on big-endian ARM systems (but may work on MIPS). The only one currently not using the generic helpers is blackfin, which is fixed to little endian. > Note that sunxi needs this function because of the register address > translation the sunxi_musb_readb / writeb wrappers are doing which > does not know how to deal with fifo data, and besides that it should > make the generic read / write fifo helpers somewhat faster by removing > an indirect function call. Your sunxi_musb_readw/writew functions however also are endian-safe and seem to get this part right, unlike all other platforms that use the generic __raw_*() accessors. With this patch applied, it should actually work fine, and it would work on other platforms as well if we change all __raw_*() calls outside of musb_default_write_fifo() and musb_default_read_fifo() to use *_relaxed() instead. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
