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Loic Poulain b23d599682 usb: stm32: Introduce transfer method
Transfer is an important concept of USB specification.
During a transfer, several packets can be transmitted.
Today the usb API only provides ep_read and ep_write
functions but the transfer concept is missing.

This is typically ok for basic drivers which don't have
to take care of how data is transfered/splitted.
However there are some drivers like CDC EEM, in which
transfer concept is important for packet management.

Moreover, current ep-write and ep_read method have a
different implementation in usb_dc_dw and usb_dc_stm32
device drivers. For example usb_dc_dw supports only
1-data-packet transfers due to its implementation.
This can increase latency and reduce performance.

I think this is something we need to fix/improve by
implementing better transfer management.

This patch introduces usb_dc_ ep_transfer method which
can be used to configure IN/OUT transfers. This allows
to configure and request different transfer sizes and
should prevent usage of the current stm32 temporary
buffer.

This method has asynchronous and synchronous mode.
Synchronous mode waits for transfer completion before
returning. Asynchronouse mode (irq safe) configures
the transfer and returns immediately, the provided
callback will be then called on transfer completion.

This also update ep_write and ep_read stm32 implementation
to use this new method but keep their behavior unchanged
for legacy reasons.

Note that for now this method is local to stm32 device
driver, however the goal would be to expose this function
as a new USB device driver API method so that class
drivers use it. This will request same implementation in
the usb_dc_dw_driver.

Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
2018-01-29 11:26:48 -06:00
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