Re: [PATCH 2/2] spi: spi-ti-qspi: Handle truncated frames properly

[Ben Hutchings <ben.hutchings-4yDnlxn2s6sWdaTGBSpHTA@public.gmane.org>]

On Tue, 2016-04-12 at 02:58 +0100, Mark Brown wrote:
> On Tue, Apr 05, 2016 at 08:48:48PM +0100, Ben Hutchings wrote:
> 
> > We clamp frame_length to a maximum of 4096, but do not limit the
> > number of words written or read properly.  This causes 4K reads (which
> > some m25p80-like flash chips support) to return garbage for the last
> > few bytes.
> 
> > Recalculate the length of each transfer, taking the frame length into
> > account.  Use this length in qspi_{read,write}_msg(), and to increment
> > spi_message::actual_length.
> 
> I'm having a hard time understanding what's actually wrong here or how
> this change is intended to fix it,

"4K reads...return garbage"  That's wrong, no?

> I think again because I don't know
> what frame_length is intended to be.  As far as I can tell frame_length
> is the number of words we're going to transfer in the entire message

Yes.

> and the driver has in some places been mixing up words and bytes

No, it's been completely ignoring the (potentially truncated)
frame_length and using the original transfer lengths for each transfer.

> which is
> causing the breakage so the intention is to consistently use words
> throught the driver.  Is that correct?

No.

I'll add a renaming of variables to make it clearer.

Ben.

> > -		ret = qspi_transfer_msg(qspi, t);
> > +		wlen = t->bits_per_word >> 3;
> 
> For the benefit of readers:
> 
> 	wlen = t->bits_per_word / 8.

-- 
Ben Hutchings
Software Developer, Codethink Ltd.


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