On 02/28/2014 12:47 PM, David Laight wrote: > From: Geert Uytterhoeven >> On Fri, Feb 28, 2014 at 12:37 PM, Marc Kleine-Budde wrote: >>>>> A 32 bit read/modify/write is a standard operation, nothing special, no >>>>> need to worry about byte swapping or anything like this. >>>> >>>> Oh, really? 8-) >>>> Don't you know that read[bwlq]() assume little-endian memory layout >>>> and to read from big-endian 32-bit register one normally needs readl_be()? >>> >>> I assume you are on little endian ARM only (for now). >>> >>> If you use a standard 32 bit read, then modify the correct bits in that >>> 32 bit word and write it back, with the corresponding 32 bit write >>> everything should be fine. For this usecase you just have yo figure out >>> which 24 of the 32 bit are the one you have to change and which are the >>> 8 that must not be modified. >>> >>> Looking at the register layout: >>> >>>> + u8 bcr[3]; /* Bit Configuration Register */ >>>> + u8 clkr; /* Clock Select Register */ >>> >>> I think clkr would be the lowest 8 bit and bcr[] are the upper 24. >> >> That would be the outcome on big endian ;-) > > Looks to me as though it should be defined as a 32bit field and then > the appropriate bit definitions and masks applied. Ack, 32bit yes, but no field (as in http://en.wikipedia.org/wiki/Bit_field). Marc -- Pengutronix e.K. | Marc Kleine-Budde | Industrial Linux Solutions | Phone: +49-231-2826-924 | Vertretung West/Dortmund | Fax: +49-5121-206917-5555 | Amtsgericht Hildesheim, HRA 2686 | http://www.pengutronix.de |