Nouveau - Sep 2025 - [PATCH v4 1/6] nova-core: bitfield: Move bitfield-specific code from register! into new macro

On Mon, Sep 29, 2025 at 03:26:57PM -0400, Joel Fernandes
wrote:
> On 9/24/2025 12:40 PM, Greg KH wrote:
> > On Tue, Sep 23, 2025 at 06:24:34PM -0400, Joel Fernandes wrote:
> [..]
> > 
> >> For the separate issue of enforcing endianness with respect to
(across)
> >> multiple fields, I agree with you that if the user's backend
(the consumer of
> >> the data) is not doing such conversion, say via regmap, then that
becomes a
> >> problem. But that problem is orthogonal/different and cannot be
solved here.
> > 
> > But that is exactly what these macros are being defined here for, so
to
> > ignore that is going to cause problems :)
> > 
> 
> If needed, happy to add endianness support as needed by providing
additional
> options to the macro. Based on this thread, it sounds like we want see if
that
> is really needed here or can be solved elsewhere (?). The mental model I
kind of
> have is this macro should only be dealing with CPU native endianness, much
like
> bitfields in C deal with CPU endianness. Hmm.
Just don't go down the old path like drivers/net/fddi/skfp/h/supern_2.h
does with it's definition of:

	union tx_descr {
		struct {
	#ifdef  LITTLE_ENDIAN
		unsigned int    tx_length:16 ;  /* frame length lower/upper byte */
		unsigned int    tx_res   :8 ;   /* reserved      (bit 16..23) */
		unsigned int    tx_xmtabt:1 ;   /* transmit abort */
		unsigned int    tx_nfcs  :1 ;   /* no frame check sequence */
		unsigned int    tx_xdone :1 ;   /* give up token */
		unsigned int    tx_rpxm  :2 ;   /* byte offset */
		unsigned int    tx_pat1  :2 ;   /* must be TXP1 */
		unsigned int    tx_more  :1 ;   /* more frame in chain */
	#else
		unsigned int    tx_more  :1 ;   /* more frame in chain */
		unsigned int    tx_pat1  :2 ;   /* must be TXP1 */
		unsigned int    tx_rpxm  :2 ;   /* byte offset */
		unsigned int    tx_xdone :1 ;   /* give up token */
		unsigned int    tx_nfcs  :1 ;   /* no frame check sequence */
		unsigned int    tx_xmtabt:1 ;   /* transmit abort */
		unsigned int    tx_res   :8 ;   /* reserved      (bit 16..23) */
		unsigned int    tx_length:16 ;  /* frame length lower/upper byte */
	#endif
		} t ;
		long    i ;
	} ;

CPU endinness, hah, as if...