[U-Boot] [PATCH 4/6] usb:udc:samsung: Zero copy approach for data passed to Samsung's UDC driver

Lukasz Majewski
2014-02-01T11:05:29Z

On Sat, 1 Feb 2014 03:55:20 +0100
Marek Vasut <marex@denx.de> wrote:

> On Friday, January 31, 2014 at 01:16:27 PM, Lukasz Majewski wrote:
> > The Samsung's UDC driver is not anymore copying data from USB
> > requests to data aligned internal buffers. Now it works directly in
> > data allocated in the upper layers like UMS, DFU, THOR.
> >
> > This change is possible since those gadgets now take care to
> > allocate buffers aligned to cache line (CONFIG_SYS_CACHELINE_SIZE ).
> >
> > Previously the UDC needed to copy this data to internal aligned
> > buffer to prevent from unaligned access exceptions.
> >
> > Test condition
> > - test HW + measurement: Trats - Exynos4210 rev.1
> > - test HW Trats2 - Exynos4412 rev.1
> > 400 MiB compressed rootfs image download with `thor 0 mmc 0`
> >
> > Measurement:
> > Transmission speed: 27.04 MiB/s
> >
> > Change-Id: I1df1fbafc72ec703f0367ddee3fedf3a3f5523ed
> > Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
> > Cc: Marek Vasut <marex@denx.de>
>
> You should use ROUND_UP(), not ROUND() throughout the patch.
> Otherwise you might fail to flush/invalidate the last little bit of
> data in some cacheline.

I might overlooked something, so please correct me if needed.

I allocate buffers in gadgets which are aligned to cache line with
starting address and its size is a multiplication of cache line size
(so I will not trash data allocated next to it when I invalidate cache).

In the code I'm using ROUND to invalidate/flush more data than needed
(ROUND(176, 32) = 192). I'm prepared for this since buffer in gadget is
properly allocated (with DEFINE_CACHE_ALIGN_BUFFER() which uses
roundup() internally).

Best regards,
Lukasz Majewski

>
> Best regards,
> Marek Vasut
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