Re: [PATCH v2] USB: Add MSM USB Device Controller driver

[Pavan Kondeti <pkondeti@codeaurora.org>]

Hi Dave,

On 11/28/2010 12:00 PM, David Brownell wrote:
>
>> implementing specific hooks needed for MSM. I am relying on
>> gadget_is_xxx() macro for MSM specific workarounds.
>
> NEVER DO THAT from inside controller drivers.

Here we are using the macro in ci13xxx_udc core which is included by
two gadget controller drivers.

>
> (If the code isn't specific to the msm silicon, and works on
> other vendors' implementations too, it'd misbehave anyway.
>
> Those calls are for gadget drivers, e.g. to embed knowledge about
> controller issues which can't be detected by looking at
> what's advertised by the gadget controller device.  Using them isn't
> encouraged.
>
>
> Controller drivers should see what hardware they're talking to by
> actually talking to the chip  and detecting any quirks (be they
> revision-specific or otherwise).  In some cases platform_data will
> be the way to package such information.
>

We need the following hooks/extension in ci13xxx_udc for MSM SoC.

1. MSM USB device controller depends on OTG driver for clocks, Low power 
mode,
and PHY initialization. So udc_probe() must fail if 
otg_get_transceiver() fails.
2. By default streaming mode is enabled in ci13xxx controller. It has to be
disabled due to some known issues.
3. Currently, pull-up is enabled upon gadget driver registration. But we 
want
to enable only upon VBUS presence. also controller must be reset before 
enabling
the pull-up as the controller was in host mode before.
4. Hardware registers should not be accessed in udc_probe()

I have started with flags to achieve the above and ended up with following:

TRANSCEIVER_IS_REQUIRED: Fail udc_probe() if otg_get_transceiver() == NULL
SKIP_RESET_IN_PROBE: avoid resetting the hardware in udc_prob()
ENABLE_PULLUP_UPON_VBUS: Enable pull-up upon VBUS
RESET_BEFORE_PULLUP: Reset the hardware before pull-up
DISABLE_STREAM_MODE: Disable streaming mode
A post reset callback to write into special registers after reset

I thought introducing this many flags may not be a good idea and used 
gadget_is_xxx()
macro to achieve the same. if tomorrow, some gadget controller wants to 
fail udc_probe()
if otg_get_tranceiver(), they can too OR their gadget_is_xxx() macro. If 
you say using
flags is not _bad_, I will take that approach.

Thanks,
Pavan

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