[PATCH 00/14] archosg9: add support for tablet

[Sascha Hauer]

On Fri, Oct 12, 2012 at 02:55:18AM +0200, vj wrote:
> > Ups, missed that. That's really a huge speed gain. I wonder why this
> > happens. Maybe the overhead of request/release sdram region is
> > significant with MMU disabled. Could you play with the BUFSIZ parameter
> > to see if there's a good compromise between speeding up your transfer
> > and still sensible buffer sizes?
> 
> Here are the results:
> 13133*PAGE_SIZE: Transferred 53789775 bytes in 3.326747 seconds at
> 15.419848 MBps
>    64*PAGE_SIZE: Transferred 53789775 bytes in 3.478078 seconds at
> 14.748928 MBps
>    32*PAGE_SIZE: Transferred 53789775 bytes in 3.655790 seconds at
> 14.031968 MBps
>    16*PAGE_SIZE: Transferred 53789775 bytes in 3.987313 seconds at
> 12.865286 MBps
>     8*PAGE_SIZE: Transferred 53789775 bytes in 4.540697 seconds at
> 11.297368 MBps
>     4*PAGE_SIZE: Transferred 53789775 bytes in 5.876598 seconds at
> 8.729188 MBps
>     2*PAGE_SIZE: Transferred 53789775 bytes in 8.249404 seconds at
> 6.218380 MBps
> Note: 13133 is reading the file at once.

So 32 * PAGE_SIZE could be a good compromise. That is still a fine
enough granularity for requesting SDRAM regions.

> 
> >
> > BTW I wonder if it would be possible to use the MMU in your setup. We
> > have a 1:1 flat mapping which should be no problem for the ROM code.
> > You probably would have to use dma_alloc_coherent to allocate the
> > buffers which are used for USB transfers.
> 
> Tested with MMU enabled having the buffers on local stack: fail
> with buffers allocated with xzalloc: fail
> with dma_alloc_coherent: fail
> all of them freezes when calling the ROM function
> omap4_usbboot_pdata.io->write(...)
> also tried this initcalls, all with same result:
> core_initcall(omap4_usbboot_init);
> postmmu_initcall(omap4_usbboot_init);
> 
> Why it doesn't work? I don't know. But if anybody wants to investigate attached
> is the ROM code. At the top of the file are the entry points used by
> barebox, which
> surely are wrong because aren't dword aligned!

I have no idea. That's probably the point where a jtag debugger could
help.

Sascha

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