Hi Arnd, On Wed, Aug 15, 2012 at 02:30:01PM +0100, Arnd Bergmann wrote: > On Tuesday 14 August 2012, Catalin Marinas wrote: > > +/* > > + * TCR flags. > > + */ > > +#define TCR_TxSZ(x) (((64 - (x)) << 16) | ((64 - (x)) << 0)) > > +#define TCR_IRGN_NC ((0 << 8) | (0 << 24)) > > +#define TCR_IRGN_WBWA ((1 << 8) | (1 << 24)) > > +#define TCR_IRGN_WT ((2 << 8) | (2 << 24)) > > +#define TCR_IRGN_WBnWA ((3 << 8) | (3 << 24)) > > +#define TCR_IRGN_MASK ((3 << 8) | (3 << 24)) > > +#define TCR_ORGN_NC ((0 << 10) | (0 << 26)) > > +#define TCR_ORGN_WBWA ((1 << 10) | (1 << 26)) > > +#define TCR_ORGN_WT ((2 << 10) | (2 << 26)) > > +#define TCR_ORGN_WBnWA ((3 << 10) | (3 << 26)) > > +#define TCR_ORGN_MASK ((3 << 10) | (3 << 26)) > > +#define TCR_SHARED ((3 << 12) | (3 << 28)) > > +#define TCR_TG0_64K (1 << 14) > > +#define TCR_TG1_64K (1 << 30) > > +#define TCR_IPS_40BIT (2 << 32) > > +#define TCR_ASID16 (1 << 36) > > + > > As a matter of coding style, I would much prefer tables like this to be > written as > > #define TCR_IRGN_MASK 0x0000000003000300 > #define TCR_IRGN_WBnWA 0x0000000003000300 > #define TCR_IRGN_WT 0x0000000002000200 > #define TCR_IRGN_WBWA 0x0000000001000100 > #define TCR_IRGN_NC 0x0000000000000000 > > #define TCR_ORGN_MASK 0x000000000c000c00 > #define TCR_ORGN_WBnWA 0x000000000c000c00 > #define TCR_ORGN_WT 0x0000000008000800 > #define TCR_ORGN_WBWA 0x0000000004000400 > #define TCR_ORGN_NC 0x0000000000000000 > > The advantage of this is that you can visually compare the bitmasks > to a hex dump, and if you are suffering from endian-confused documentation > authors, there is no ambiguity about which end of the word is bit zero.
That depends on the case, in some places it's more readable like this. In the above case, I find it easier to compare against the documentation which, for example, has groups of 2 bits at position 8 and 24 or 10 and 26 (for TTBR0 and TTBR1). The meaning of a group of 2 bits is described separately as 0b00 (NC), 0b01(WBWA) etc. Same goes for the shareability bits (12 and 28). So I think at least for code writing it's less error-prone to write the explicit bit position than a magic long hex. -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
