On 23. 4. 19. 17:14, Krzysztof Kozlowski wrote:
> On 19/04/2023 08:06, Jaewon Kim wrote:
>> Adds cpu_relax() to prevent long busy-wait.
> How cpu_relax prevents long waiting?
As I know, cpu_relax() can be converted to yield. This can prevent
excessive use of the CPU in busy-loop.
I'll replace poor sentence like below in v3.
("Adds cpu_relax() to allow CPU relaxation in busy-loop")
>> There is busy-wait loop to check data transfer completion in polling mode.
>>
>> Signed-off-by: Jaewon Kim<jaewon02.kim@xxxxxxxxxxx>
>> ---
>> drivers/spi/spi-s3c64xx.c | 1 +
>> 1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/spi/spi-s3c64xx.c b/drivers/spi/spi-s3c64xx.c
>> index 273aa02322d9..886722fb40ea 100644
>> --- a/drivers/spi/spi-s3c64xx.c
>> +++ b/drivers/spi/spi-s3c64xx.c
>> @@ -568,6 +568,7 @@ static int s3c64xx_wait_for_pio(struct s3c64xx_spi_driver_data *sdd,
>>
>> val = msecs_to_loops(ms);
>> do {
>> + cpu_relax();
> Shouldn't this be just readl_poll_timeout()? Or the syntax would be too
> complicated?
I think we can replace this while() loop to readl_poll_timeout().
However, we should use 0 value as 'delay_us' parameter. Because delay
can affect throughput.
My purpose is add relax to this busy-loop.
we cannot give relax if we change to readl_poll_timeout().
>> status = readl(regs + S3C64XX_SPI_STATUS);
>> } while (RX_FIFO_LVL(status, sdd) < xfer->len && --val);
>>
> Best regards,
> Krzysztof
>
>
Thanks
Jaewon Kim
