Re: [PATCH v3 2/3] bus: mhi: core: Move to polling method to wait for MHI ready

Bhaumik Bhatt
2021-03-10T22:59:43Z

On 2021-03-10 11:02 AM, Jeffrey Hugo wrote:
> On 2/23/2021 8:44 PM, Bhaumik Bhatt wrote:
>> In certain devices, it is likely that there is no incoming MHI
>> interrupt for a transition to MHI READY state. One such example
>> is the move from Pass Through to an SBL or AMSS execution
>> environment. In order to facilitate faster bootup times as there
>> is no need to wait until timeout_ms completes, MHI host can poll
>> every 25 milliseconds to check if device has entered MHI READY
>> until a maximum timeout of twice the timeout_ms is reached.
>>
>> Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>
>> ---
>> drivers/bus/mhi/core/pm.c | 31 ++++++++++++++-----------------
>> 1 file changed, 14 insertions(+), 17 deletions(-)
>>
>> diff --git a/drivers/bus/mhi/core/pm.c b/drivers/bus/mhi/core/pm.c
>> index 681960c..5fe33d4 100644
>> --- a/drivers/bus/mhi/core/pm.c
>> +++ b/drivers/bus/mhi/core/pm.c
>> @@ -153,34 +153,31 @@ static void mhi_toggle_dev_wake(struct
>> mhi_controller *mhi_cntrl)
>> /* Handle device ready state transition */
>> int mhi_ready_state_transition(struct mhi_controller *mhi_cntrl)
>> {
>> - void __iomem *base = mhi_cntrl->regs;
>> struct mhi_event *mhi_event;
>> enum mhi_pm_state cur_state;
>> struct device *dev = &mhi_cntrl->mhi_dev->dev;
>> - u32 reset = 1, ready = 0;
>> int ret, i;
>> - /* Wait for RESET to be cleared and READY bit to be set by the
>> device */
>> - wait_event_timeout(mhi_cntrl->state_event,
>> - MHI_PM_IN_FATAL_STATE(mhi_cntrl->pm_state) ||
>> - mhi_read_reg_field(mhi_cntrl, base, MHICTRL,
>> - MHICTRL_RESET_MASK,
>> - MHICTRL_RESET_SHIFT, &reset) ||
>> - mhi_read_reg_field(mhi_cntrl, base, MHISTATUS,
>> - MHISTATUS_READY_MASK,
>> - MHISTATUS_READY_SHIFT, &ready) ||
>> - (!reset && ready),
>> - msecs_to_jiffies(mhi_cntrl->timeout_ms));
>> -
>> /* Check if device entered error state */
>> if (MHI_PM_IN_FATAL_STATE(mhi_cntrl->pm_state)) {
>> dev_err(dev, "Device link is not accessible\n");
>> return -EIO;
>> }
>> - /* Timeout if device did not transition to ready state */
>> - if (reset || !ready) {
>> - dev_err(dev, "Device Ready timeout\n");
>> + /* Wait for RESET to be cleared and READY bit to be set by the
>> device */
>> + ret = mhi_poll_reg_field(mhi_cntrl, mhi_cntrl->regs, MHICTRL,
>> + MHICTRL_RESET_MASK, MHICTRL_RESET_SHIFT, 0,
>> + 25000);
>> + if (ret) {
>> + dev_err(dev, "Device failed to clear MHI Reset\n");
>> + return -ETIMEDOUT;
>> + }
>> +
>> + ret = mhi_poll_reg_field(mhi_cntrl, mhi_cntrl->regs, MHISTATUS,
>> + MHISTATUS_READY_MASK, MHISTATUS_READY_SHIFT, 1,
>> + 25000);
>
> You use the magic number "25000" twice here. Its my understanding
> that the preference is to inline a magic number if its used in one
> spot, but use a macro if its used more than that.
>
> Both uses are confined to this function, and in close proximity, so
> chances that one gets updated without the other seem minimal, so this
> feels like a borderline case. I don't know if Mani has an opinion
> here.
>
> I'd probably err on the side of making a macro or a single variable.
> If not, I think some comments explaining the value are warranted
> (should comment the macro as well).
>
I think just using a variable would be good enough here. I can add a
comment
when defining the interval variable.
>> + if (ret) {
>> + dev_err(dev, "Device failed to enter MHI Ready\n");
>> return -ETIMEDOUT;
>> }
>>

Thanks,
Bhaumik
---
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora
Forum,