Arnd Bergmann a écrit :
> On Friday 31 August 2012, Stephen Boyd wrote:
>>> +static int hvc_dcc_put_chars_v6(uint32_t vt, const char *buf, int count)
>>> +{
>>> + int i;
>>> +
>>> + for (i = 0; i < count; i++) {
>>> + while (__dcc_getstatus_v6() & DCC_STATUS_TX_V6)
>>> + cpu_relax();
>>> +
>>> + __dcc_putchar_v6(buf[i]);
>>> + }
>>> +
>>> + return count;
>>> +}
>> It's unfortunate that the main logic is duplicated. I wonder if we could
>> push the runtime decision slightly lower into the accessor functions
>> instead and make some new functions dcc_tx_busy() and dcc_rx_busy() or
>> something. Then these loops stay the same.
The code is so small (30 asm + 30 C code) that I wonder if worth adding
complexity in the code.
Also calling cpu_architecture isn't free and if the want to put the runtime
decision into the hot path, this means we need to cache the result.
>
> Agreed. Ideally, you should be able to get the code to be compiled into
> the same binary as before for ARMv6+. If only the inline assembly differs,
> you can do something like
>
> static inline char __dcc_getchar(void)
> {
> char __c;
>
> if (__LINUX_ARM_ARCH >= 6)
> asm volatile("mrc p14, 0, %0, c0, c5, 0 @ read comms data reg"
> : "=r" (__c));
> else
> asm volatile ("mrc p14, 0, %0, c1, c0 @ read comms data reg"
> : "=r" (ret));
> isb();
>
> return __c;
> }
>
> Arnd
>
Yes doing that will be great!
But Alan wanted "all be runtime handled".
May be we can do something like:
static int cpu_arch;
static inline char __dcc_getchar(void)
{
char __c;
if (cpu_arch >= 6)
asm volatile("mrc p14, 0, %0, c0, c5, 0 @ read comms data reg"
: "=r" (__c));
else
asm volatile ("mrc p14, 0, %0, c1, c0 @ read comms data reg"
: "=r" (ret));
isb();
return __c;
}
static int __init hvc_dcc_console_init(void)
{
cpu_arch = cpu_architecture();
...
}
Matthieu
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