Re: [PATCH v7 2/2] mmc: sdhci-msm: Initial support for MSM chipsets

[Georgi Djakov <gdjakov@mm-sol.com>]

On 12/09/2013 11:46 AM, Mark Rutland wrote:
>>> [...]
>>>
>>>> +       /*
>>>> +        * CORE_SW_RST above may trigger power irq if previous status of PWRCTL
>>>> +        * was either BUS_ON or IO_HIGH_V. So before we enable the power irq
>>>> +        * interrupt in GIC (by registering the interrupt handler), we need to
>>>> +        * ensure that any pending power irq interrupt status is acknowledged
>>>> +        * otherwise power irq interrupt handler would be fired prematurely.
>>>> +        */
>>>> +       irq_status = readl_relaxed(msm_host->core_mem + CORE_PWRCTL_STATUS);
>>>> +       writel_relaxed(irq_status, (msm_host->core_mem + CORE_PWRCTL_CLEAR));
>>>> +       irq_ctl = readl_relaxed(msm_host->core_mem + CORE_PWRCTL_CTL);
>>>> +       if (irq_status & (CORE_PWRCTL_BUS_ON | CORE_PWRCTL_BUS_OFF))
>>>> +               irq_ctl |= CORE_PWRCTL_BUS_SUCCESS;
>>>> +       if (irq_status & (CORE_PWRCTL_IO_HIGH | CORE_PWRCTL_IO_LOW))
>>>> +               irq_ctl |= CORE_PWRCTL_IO_SUCCESS;
>>>> +       writel_relaxed(irq_ctl, (msm_host->core_mem + CORE_PWRCTL_CTL));
>>>> +       /*
>>>> +        * Ensure that above writes are propogated before interrupt enablement
>>>> +        * in GIC.
>>>> +        */
>>>> +       mb();
>>>
>>> Does this guarantee that the device has finished responding to the write
>>> and deasserted the interrupt line (i.e. does the device only acknowledge
>>> the write once that is true)?
>>>
>>
>> I am not sure that i understand your concern. The write to
>> CORE_PWRCTL_CTL should acknowledge and deassert the interrupt.
>
> The mb() ensures that the write has reached the device, and the device's
> slave interface has acknowledged the write. On some devices this
> acknowledgement of the write can be asynchronous with respect to the
> device changing state in response to the write (i.e. the interrupt might
> get deasserted a short time after the write completes). Typically there
> is a register that should be polled to see whether the state change has
> completed.
>
> Does the acknowledgement of the write only occur once the device has
> changed state? Or might it change state in the background?
>

Thanks for clarifying this. All this is correct, but it will be 
difficult to answer, because i don't have documentation and i can only 
be guessing how exactly the hardware behaves internally.
I can remove this fragment from the initial version to keep it more 
simple. Meanwhile i can do some tests reading/polling the status 
register to see how and when exactly it changes.

Thanks,
Georgi