[U-Boot] [PATCH 1/2] common: make bouncebuf work for non-DMA transfers

[Goldschmidt Simon]

Hi Vignesh,

Vignesh R wrote:
> [..]
> Its not actually unaligned access, cadence QSPI IP on TI platforms do
> not support non-byte accesses except for the last word. As per the TRM:
> "The external master is only permitted to issue 32-bit data interface
> writes until the last word of an indirect
> transfer"

OK, I thought it was unaligned access because of reading your commit
message talking about data aborts. But this was in the write part
indeed.

>> So given my explanation above, what's the preferred way to fix this?
> 
> Sorry, I overlooked the fact that bounce_buffer_stop() is calling
> invalidate_dcache_range(). Somehow, this did not show problems on my
> platform although its a writeback cache.
>
> I would suggest to revert commit b63b46313 ("spi: cadence_qspi_apb: Use
> 32 bit indirect read transaction when possible"). I have seen that non
> 32 bit accesses cause problems only while writing to flash but not
> during read operations although the TRM states that both reads and
> writes are affected.
> But, since reverting b63b46313 as such does not break TI platforms, I
> would prefer sending a revert.
> Meanwhile, I will work on a better patch later.

I have not actually tested writing with dcache enabled, but from
reading the code, it should not be a problem. I'll test that then.

> Lets not touch bouncebuf for now.

OK. I take it that bouncebuf should be only used for dma transfers.
In that case, shouldn't we revert the write patch, too, eventually?
Even if it does not break data consistency like in the read direction,
messing around with the cache while doing cpu transfers at the very
least will drop performance. Plus it seems like a bad example.

We can do that later, of course, as it should work like it is now.

>> I need this driver fixed, so whatever way will be accepted is fine by
>> me, I guess. Just let me know.
>> 
>
> Sorry for the trouble. I am okay with reverting the patch affecting read
> path.

OK. I'll send a patch hat reverts the read path then.

Thank you for your help!

Regards,
Simon