[PATCH v6 15/16] OMAP2+: UART: Enable back uart clocks with runtime API for early console

[Govindraj]

On Thu, Oct 13, 2011 at 5:30 AM, Kevin Hilman <khilman at ti.com> wrote:
> Govindraj <govindraj.ti at gmail.com> writes:
>
>> On Wed, Oct 12, 2011 at 2:36 AM, Kevin Hilman <khilman at ti.com> wrote:
>>> "Govindraj.R" <govindraj.raja at ti.com> writes:
>>>
>>>> For the early console probing we had avoided hwmod reset and idling
>>>> and uart was idled using hwmod API and enabled back using omap_device API
>>>> after omap_device registration.
>>>>
>>>> Now since we are using runtime API's to enable back uart, move hwmod
>>>> idling and use runtime API to enable back UART.
>>>>
>>>> Signed-off-by: Govindraj.R <govindraj.raja at ti.com>
>>>
>>> Now that the driver is using runtime PM.  Why do we still need
>>> HWMOD_INIT_NO_IDLE and HWMOD_INIT_NO_RESET?
>>>
>>> The comment in the code says:
>>>
>>>                /*
>>>                 * During UART early init, device need to be probed
>>>                 * to determine SoC specific init before omap_device
>>>                 * is ready.  Therefore, don't allow idle here
>>>                 */
>>>
>>> This was true when using the 8250 driver because it was not using
>>> runtime PM so could not know how to (re)enable the device.
>>>
>>> However, since the driver is now runtime PM adapted, any device access
>>> should be contained within a runtime PM get/put block, so there should
>>> no longer be a reason not allow the IP blocks to be reset during boot.
>>>
>>
>> Forgot to add, this is still needed for
>> earlyprintk(CONFIG_EARLY_PRINTK) use case,
>
> Ah, right.  I forgot about that.  Please update the changelog (and
> comment in the code) to reflect that.
>
>> The initial boot prints until a console driver is available is from
>> "arch/arm/kernel/early_printk.c" which does a tx on uart console
>> and relies on configuration from bootloader.
>>
>> during bootup earlyprink does a tx on uart console and if  uart driver
>> is not available yet
>> uart reset or idle done by hwmod layer can cause boot failures.
>>
>> --> put_char from earlyprintk.c
>>      --> reset/idle from hwmod layer
>>           --> put_char from earlyprintk.c
>>
>>
>> So console_uart reset or clock gating must be done only after uart
>> driver is available or be prevented using these available hwmod_flags.
>
> So why not leave the driver out of it and solve it like the current code
> does?
>
> The current codes use the hwmod flags, then waits until the UART driver
> is available (after omap_device_build) and uses omap_hwmod_idle() to do
> an clean idle of the device.
>
> Notably this is inside a console_lock/console_unlock block so that
> prints are buffered.
>
> The current code then does an omap_device_enable() to re-enable the
> device, but you shouldn't need that after the driver is converted to
> runtime PM.

Yes similar approach here, We are not doing hwmod idle
until console driver is available, once omap-serial is available
from probe doing hwmod_idle* and then get_sync.

hwmod idle in serial.c will still cause problems if ealryprintk tries to print
until omap-uart console driver is not available, as now with rumtime adaptation
only driver can enable back clocks. So have added a function pointer
to pdata which
calls hwmod_idle implemented in serial.c calling omap_hwmod_idle.

--
Thanks,
Govindraj.R

*function pointer implemented in serial.c not directly calling
omap_hmwod_idle API.