Re: [PATCH] serial: DCC(JTAG) serial and console emulation support

[Daniel Walker <dwalker@codeaurora.org>]

On Wed, 2010-10-06 at 11:21 -0400, Nicolas Pitre wrote:

> static inline char
> __dcc_getchar(void)
> {
>      char __c;
> 
> #if !defined(CONFIG_CPU_V7)
>      asm("mrc p14, 0, %0, c0, c5, 0  @ read comms data reg"
>              : "=r" (__c) : : "cc");
> #else
>      asm(
>      "get_wait:      mrc p14, 0, pc, c0, c1, 0                       \n\
>                      bne get_wait                                    \n\
>                      mrc p14, 0, %0, c0, c5, 0       @ read comms data reg"
>              : "=r" (__c) : : "cc");
> #endif
> 
>      return __c;
> }
> 
> static inline void
> __dcc_putchar(char c)
> {
> #if !defined(CONFIG_CPU_V7)
>      asm("mcr p14, 0, %0, c0, c5, 0  @ write a char"
>              : /* no output register */
>              : "r" (c) : "cc");
> #else
>      asm(
>      "put_wait:      mrc p14, 0, pc, c0, c1, 0                   \n\
>                      bcs put_wait                                \n\
>                      mcr p14, 0, %0, c0, c5, 0                   "
>      : : "r" (c) : "cc");
> #endif
> }
> 
> To me the above is easier to read.  Not a big deal since the functions 
> are rather small, but still an improvement.  Searching for __dcc_putchar 
> would produce a single hit, and if the prototype has to change it is 
> done in only one place, etc.

It makes the internals of the function much more busy. There's more
stuff that could be executing that you have to think about while
reviewing the function.

> BTW the cc clobber in the asm for __dcc_putchar() is unneeded.

Without it caused a crash in __dcc_getchar() ..

Daniel

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