On Mon, 20 Dec 2010, Stephen Boyd wrote:
> The inline assembly differences for v6 vs. v7 in the hvc_dcc
> driver are purely optimizations. On a v7 processor, an mrc with
> the pc sets the condition codes to the 28-31 bits of the register
> being read. It just so happens that the TX/RX full bits the DCC
> driver is testing for are high enough in the register to be put
> into the condition codes. On a v6 processor, this "feature" isn't
> implemented and thus we have to do the usual read, mask, test
> operations to check for TX/RX full.
>
> Since we already test the RX/TX full bits before calling
> __dcc_getchar() and __dcc_putchar() we don't actually need to do
> anything special for v7 over v6. The only difference is in
> hvc_dcc_get_chars(). We would test RX full, poll RX full, and
> then read a character from the buffer, whereas now we will test
> RX full, read a character from the buffer, and then test RX full
> again for the second iteration of the loop. It doesn't seem
> possible for the buffer to go from full to empty between testing
> the RX full and reading a character. Therefore, replace the v7
> versions with the v6 versions and everything works the same.
>
> Cc: Tony Lindgren <tony@xxxxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Nicolas Pitre <nicolas.pitre@xxxxxxxxxx>
> Cc: Daniel Walker <dwalker@xxxxxxxxxxxxxx>
> Signed-off-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
Acked-by: Nicolas Pitre <nicolas.pitre@xxxxxxxxxx>
> ---
> drivers/char/hvc_dcc.c | 24 ------------------------
> 1 files changed, 0 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/char/hvc_dcc.c b/drivers/char/hvc_dcc.c
> index ad23cc8..435f6fa 100644
> --- a/drivers/char/hvc_dcc.c
> +++ b/drivers/char/hvc_dcc.c
> @@ -40,19 +40,6 @@ static inline u32 __dcc_getstatus(void)
> }
>
>
> -#if defined(CONFIG_CPU_V7)
> -static inline char __dcc_getchar(void)
> -{
> - char __c;
> -
> - asm volatile("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");
> -
> - return __c;
> -}
> -#else
> static inline char __dcc_getchar(void)
> {
> char __c;
> @@ -62,24 +49,13 @@ static inline char __dcc_getchar(void)
>
> return __c;
> }
> -#endif
>
> -#if defined(CONFIG_CPU_V7)
> -static inline void __dcc_putchar(char c)
> -{
> - asm volatile("put_wait: mrc p14, 0, pc, c0, c1, 0 \n\
> - bcs put_wait \n\
> - mcr p14, 0, %0, c0, c5, 0 "
> - : : "r" (c) : "cc");
> -}
> -#else
> static inline void __dcc_putchar(char c)
> {
> asm volatile("mcr p14, 0, %0, c0, c5, 0 @ write a char"
> : /* no output register */
> : "r" (c));
> }
> -#endif
>
> static int hvc_dcc_put_chars(uint32_t vt, const char *buf, int count)
> {
> --
> Sent by an employee of the Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
>
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