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SubjectRe: [PATCH v2 07/36] platform/x86: intel_scu_ipc: Sleeping is fine when polling
On Wed, Jan 08, 2020 at 02:41:32PM +0300, Mika Westerberg wrote:
> There is no reason why the driver would need to block other threads from
> running the CPU while it is waiting for the SCU IPC to complete its
> work. For this reason switch the driver to use usleep_range() instead
> with a bit more relaxed polling loop.

I agree on this and if somebody finds a race condition that had been hidden by
the original code it will mean that somewhere else something is completely
broken.

>
> Also add constant for the timeout and use the same value for both
> polling and interrupt modes.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

>
> Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> ---
> drivers/platform/x86/intel_scu_ipc.c | 29 ++++++++++++++--------------
> 1 file changed, 14 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/platform/x86/intel_scu_ipc.c b/drivers/platform/x86/intel_scu_ipc.c
> index 43eaf9400c67..8db0644900a3 100644
> --- a/drivers/platform/x86/intel_scu_ipc.c
> +++ b/drivers/platform/x86/intel_scu_ipc.c
> @@ -79,6 +79,9 @@ static struct intel_scu_ipc_dev ipcdev; /* Only one for now */
> #define IPC_WRITE_BUFFER 0x80
> #define IPC_READ_BUFFER 0x90
>
> +/* Timeout in jiffies */
> +#define IPC_TIMEOUT (3 * HZ)
> +
> static DEFINE_MUTEX(ipclock); /* lock used to prevent multiple call to SCU */
>
> /*
> @@ -132,24 +135,20 @@ static inline u32 ipc_data_readl(struct intel_scu_ipc_dev *scu, u32 offset)
> /* Wait till scu status is busy */
> static inline int busy_loop(struct intel_scu_ipc_dev *scu)
> {
> - u32 status = ipc_read_status(scu);
> - u32 loop_count = 100000;
> + unsigned long end = jiffies + msecs_to_jiffies(IPC_TIMEOUT);
>
> - /* break if scu doesn't reset busy bit after huge retry */
> - while ((status & IPC_STATUS_BUSY) && --loop_count) {
> - udelay(1); /* scu processing time is in few u secods */
> - status = ipc_read_status(scu);
> - }
> + do {
> + u32 status;
>
> - if (status & IPC_STATUS_BUSY) {
> - dev_err(scu->dev, "IPC timed out");
> - return -ETIMEDOUT;
> - }
> + status = ipc_read_status(scu);
> + if (!(status & IPC_STATUS_BUSY))
> + return (status & IPC_STATUS_ERR) ? -EIO : 0;
>
> - if (status & IPC_STATUS_ERR)
> - return -EIO;
> + usleep_range(50, 100);
> + } while (time_before(jiffies, end));
>
> - return 0;
> + dev_err(scu->dev, "IPC timed out");
> + return -ETIMEDOUT;
> }
>
> /* Wait till ipc ioc interrupt is received or timeout in 3 HZ */
> @@ -157,7 +156,7 @@ static inline int ipc_wait_for_interrupt(struct intel_scu_ipc_dev *scu)
> {
> int status;
>
> - if (!wait_for_completion_timeout(&scu->cmd_complete, 3 * HZ)) {
> + if (!wait_for_completion_timeout(&scu->cmd_complete, IPC_TIMEOUT)) {
> dev_err(scu->dev, "IPC timed out\n");
> return -ETIMEDOUT;
> }
> --
> 2.24.1
>

--
With Best Regards,
Andy Shevchenko


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