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    SubjectRe: [PATCH 1/1][RESEND] Driver for the Atmel on-chip SSC on AT32AP and AT91.
    FromAndrew Victor <>
    Date20 Jul 2007 08:55:42 +0200
    hi Hans-Christian,
    
    > Just an example from sound/soc/at91/at91-ssc.c
    > 
    > rcmr =	  (( ssc_p->rcmr_period		<< 24) & AT91_SSC_PERIOD)
    > 			| (( 1				<< 16) & AT91_SSC_STTDLY)
    > 			| (( AT91_SSC_START_FALLING_RF	     ) & AT91_SSC_START)
    > 			| (( AT91_SSC_CK_RISING		     ) & AT91_SSC_CKI)
    > 			| (( AT91_SSC_CKO_NONE		     ) & AT91_SSC_CKO)
    > 			| (( AT91_SSC_CKS_DIV		     ) & AT91_SSC_CKS);
    
    Well, I didn't write the above, so it's more complex than it needs to
    be.
    
    For bitfields where the user can input any value we would usually add to
    the header:
       #define AT91_SSC_STTDLY_(x)   ((x) << 16)
       #define AT91_SSC_PERIOD_(x)   ((x) << 24)
    
    Then it can simply be re-written as:
    
    rcmr = AT91_SSC_PERIOD(ssc_p->rcmr_period)
    	| AT91_SSC_STTDLY(1)
    	| AT91_SSC_START_FALLING_RF
    	| AT91_SSC_CK_RISING
    	| AT91_SSC_CKO_NONE
    	| AT91_SSC_CKS_DIV;
    
    > Would with the header style for atmel-ssc be:
    > 
    > rcmr = SSC_BF(RCMR_PERIOD, ssc_p->rcmr_period)
    > 		| SSC_BF(RCMR_STTDLY, 1)
    > 		| SSC_BF(RCMR_START, 4)
    > 		| SSC_BF(RCMR_CKI, 1)
    > 		| SSC_BF(RCMR_CKO, 0)
    > 		| SSC_BF(RCMR_CKS, 0);
    > 
    > I find the latter more readable and compact, the user also does not need
    > to know the offset of the different bit-fields.
    
    But the user does then constantly have to refer to the datasheet to
    determine what CKI = 1 or CKS = 0 means.
    
    
    Regards,
      Andrew Victor
    
    
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