On 8/30/2023 6:14 PM, Stephen Boyd wrote:
> It's possible for the completion in ipc_wait_for_interrupt() to timeout,
> simply because the interrupt was delayed in being processed. A timeout
> in itself is not an error. This driver should check the status register
> upon a timeout to ensure that scheduling or interrupt processing delays
> don't affect the outcome of the IPC return value.
>
> CPU0 SCU
> ---- ---
> ipc_wait_for_interrupt()
> wait_for_completion_timeout(&scu->cmd_complete)
> [TIMEOUT] status[IPC_BUSY]=0
>
> Fix this problem by reading the status bit in all cases, regardless of
> the timeout. If the completion times out, we'll assume the problem was
> that the IPC_BUSY bit was still set, but if the status bit is cleared in
> the meantime we know that we hit some scheduling delay and we should
> just check the error bit.
>
> Cc: Prashant Malani <pmalani@xxxxxxxxxxxx>
> Cc: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
> Fixes: ed12f295bfd5 ("ipc: Added support for IPC interrupt mode")
> Signed-off-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>
> ---
> drivers/platform/x86/intel_scu_ipc.c | 15 +++++++++------
> 1 file changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/platform/x86/intel_scu_ipc.c b/drivers/platform/x86/intel_scu_ipc.c
> index 5a37becc65aa..2a21153e3bf3 100644
> --- a/drivers/platform/x86/intel_scu_ipc.c
> +++ b/drivers/platform/x86/intel_scu_ipc.c
> @@ -246,16 +246,19 @@ static inline int busy_loop(struct intel_scu_ipc_dev *scu)
> /* Wait till ipc ioc interrupt is received or timeout in 10 HZ */
> static inline int ipc_wait_for_interrupt(struct intel_scu_ipc_dev *scu)
> {
> - int status;
> + unsigned long time_left;
> + u8 status;
> + int err = 0;
>
> - if (!wait_for_completion_timeout(&scu->cmd_complete, IPC_TIMEOUT))
> - return -ETIMEDOUT;
> + time_left = wait_for_completion_timeout(&scu->cmd_complete, IPC_TIMEOUT);
> + if (!time_left)
> + err = -ETIMEDOUT;
Since you are not using the return value, I would not use time_left. I think the
following version is easy to read. But it is up to you.
wait_for_completion_timeout(&scu->cmd_complete, IPC_TIMEOUT)
status = ipc_read_status(scu);
if (status & IPC_STATUS_BUSY)
return -ETIMEDOUT;
if (status & IPC_STATUS_ERR)
return -EIO;
return 0;
With above fixed, you can add
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
>
> status = ipc_read_status(scu);
> - if (status & IPC_STATUS_ERR)
> - return -EIO;
> + if (!(status & IPC_STATUS_BUSY))
> + err = (status & IPC_STATUS_ERR) ? -EIO : 0;
>
> - return 0;
> + return err;
> }
>
> static int intel_scu_ipc_check_status(struct intel_scu_ipc_dev *scu)
--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer
