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

[Marek Vasut]

On Saturday, February 01, 2014 at 10:56:27 AM, Lukasz Majewski wrote:
> 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.

And you do correct cache management on those in the UDC driver or in the gadget 
driver ?
 
> This is the key speed improvement here.

This should be in the commit message really ;-)

Best regards,
Marek Vasut