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SubjectRe: [PATCH v7] Staging: comedi: convert while loop to timeout in ni_mio_common.c
On 2014-01-15 19:22, Chase Southwood wrote:
> This patch for ni_mio_common.c changes out a while loop for a timeout,
> which is preferred.
>
> Signed-off-by: Chase Southwood <chase.southwood@yahoo.com>
> ---
>
> Hartley,
> I sincerely apologize for the obvious mistake, I thought I had built it
> but clearly I made a mistake somewhere, as your observation is exactly
> correct. It is now fixed.
>
> Thanks,
> Chase Southwood
>
> 2: Changed from simple clean-up to swapping a timeout in for a while loop.
>
> 3: Removed extra counter variable, and added error checking.
>
> 4: No longer using counter variable, using jiffies instead.
>
> 5: udelay for 10u, instead of 1u.
>
> 6: Scrap udelay entirely, in favor of cpu_relax. Include asm/processor.h
> in order to use cpu_relax.
>
> 7: Fix typo (msec vs msecs).
>
> drivers/staging/comedi/drivers/ni_mio_common.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/staging/comedi/drivers/ni_mio_common.c b/drivers/staging/comedi/drivers/ni_mio_common.c
> index 457b884..ab7a74c 100644
> --- a/drivers/staging/comedi/drivers/ni_mio_common.c
> +++ b/drivers/staging/comedi/drivers/ni_mio_common.c
> @@ -55,6 +55,7 @@
> #include <linux/interrupt.h>
> #include <linux/sched.h>
> #include <linux/delay.h>
> +#include <asm/processor.h>
> #include "8255.h"
> #include "mite.h"
> #include "comedi_fc.h"
> @@ -687,12 +688,21 @@ static void ni_clear_ai_fifo(struct comedi_device *dev)
> {
> const struct ni_board_struct *board = comedi_board(dev);
> struct ni_private *devpriv = dev->private;
> + unsigned long timeout;
>
> if (board->reg_type == ni_reg_6143) {
> /* Flush the 6143 data FIFO */
> ni_writel(0x10, AIFIFO_Control_6143); /* Flush fifo */
> ni_writel(0x00, AIFIFO_Control_6143); /* Flush fifo */
> - while (ni_readl(AIFIFO_Status_6143) & 0x10) ; /* Wait for complete */
> + /* Wait for complete */
> + timeout = jiffies + msecs_to_jiffies(500);
> + while (ni_readl(AIFIFO_Status_6143) & 0x10) {
> + if (time_after(jiffies, timeout)) {
> + comedi_error(dev, "FIFO flush timeout.");
> + break;
> + }
> + cpu_relax();
> + }
> } else {
> devpriv->stc_writew(dev, 1, ADC_FIFO_Clear);
> if (board->reg_type == ni_reg_625x) {
>

Sorry this is your worst nightmare, Chase. Your patch is great and has
been modified in all the ways various people have suggested, but I don't
think it is suitable.

After examining the code, it turns out ni_clear_ai_fifo() is sometimes
called from an interrupt service routine and I don't think you can wait
for jiffies to change in that case. I think we need to go back to your
PATCH v2 and fix up the checkpatch.pl warning that Greg mentioned.

Sorry about that.

--
-=( Ian Abbott @ MEV Ltd. E-mail: <abbotti@mev.co.uk> )=-
-=( Tel: +44 (0)161 477 1898 FAX: +44 (0)161 718 3587 )=-


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