Dear Arnd, Josh Boyer suggested you might provide some insight... I'm currently looking for a solution how to provide architecture independent I/O accessor functions to U-Boot. In the past, lots of code used direct pointer accesses, relying on the idea that "volatile" would be sufficient to convince the compiler and the hardware to do what was expected; some architectures (like ARM and others) used readl() / writel(), while others (like PPC) used in_8, in_le16, in_be16, in_le32, in_be32, in_le64, in_be64 etc. As we like to borrow code from Linux, I'm trying to find out what the big plan for Linux is. My understanding is that in Linux the ioreadX() / iowriteX() / ioreadXbe() / iowriteXbe() functions are supposed to provide architecture independent I/O accessors, and that the plain ioreadX() / iowriteX() functions (without the "be") are always guaranteed to be little-endian on all architectures, while the "be" functions are, well, big-endian. Is this understanding correct? If yes, does that mean that in the future we will see more Linux code using ioreadX[be]() / iowriteX[be]()? So far I did not find much hints that support this aproach - only memory-barriers.txt has only a short sentence about these functions, with basicly no explanation. What I liked from the in_[le]X() / out_[le]X() accessors on PPC was that they allowed for type checking - the compiler would raise a warning when you used in_[le]16() to read from a 32 bit wide register. However, ioreadX[be]() / iowriteX[be]() use a void * "iomem cookie", so no type checking can be done. Basicly I have two questions: 1) Can you make a statement which direction Linux is heading to? Will more (new) code use ioreadX() / iowriteX()? 2) What would be your recommendation what we should do in U-Boot? Provide for all architectures in_8, in_le16, in_be16, in_le32, in_be32, in_le64, in_be64 etc. similar to what we have for the Power architecture, well knowing that Linux will not follow that route, or use ioreadX[be]() / iowriteX[be]() which does not provide type checking, and which eventually does not find wider use in Linux either? Or even something else - like ioreadX[be]() / iowriteX[be]() with type checking added? Thanks in advance. Best regards, Wolfgang Denk -- DENX Software Engineering GmbH, MD: Wolfgang Denk & Detlev Zundel HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd@xxxxxxx The ideal situation is to have massive computing power right at home. Something that dims the streetlights and shrinks the picture on the neighbours' TVs when you boot it up. -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
