[U-Boot] [PATCH 2/6] usb:udc:samsung: Remove redundant cache operation from Samsung UDC driver

[Lukasz Majewski]

On Sat, 1 Feb 2014 03:50:26 +0100
Marek Vasut <marex at denx.de> wrote:

> On Friday, January 31, 2014 at 01:16:25 PM, Lukasz Majewski wrote:
> > A set of cache operations (both invalidation and flush) were
> > redundant in the S3C HS OTG Samsung driver.
> > 
> > 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`
> 
> The commit message is missing a proper explanation _WHY_ were they
> redundant. I do not understand why they were redundant ... and no,
> the test you performed does not justify removal of cache management
> calls.
> 

The s3c UDC driver is in u-boot since 2011. It has been added when
at Samsung boards (s5p_goni) we didn't have cache enabled.

Then there was a transition, after which L1 was enabled. Since UDC is
co-working with gadgets on the beginning it was easier to perform the
cache management inside the UDC driver.

That is why we had to copy the buffers (since e.g. device descriptors
tends to be unaligned) - which also degraded performance.

Now, all gadget code seems to be memalign'ed and ready for direct buffer
passing (despite the two overlooked kmallocs in the mass storage
gadget - which I fix in this patch set).

To sum up:

1. s3c_udc_ep0_zlp - EP0 ZLP packets don't need to invalidate the cache
(since it is zero length transmission)

2. s3c_udc_pre_setup - cache invalidation is not needed when I setup
buffer for OUT EP0 transmission.

The above two invalidation calls had been added by me, and are mine
mistakes. Those don't contribute to transmission speed up (and shall be
regarded as a cosmetic changes)

3. setdma_rx - here I invalidate parts of the s3c UDC driver's internal
buffer. This call is not needed anymore since we reuse the buffers
passed from gadgets.

This is the key speed improvement here.

Best regards,
Lukasz Majewski

> Best regards,
> Marek Vasut
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