Re: [patch 05/14] mfd: PCAP2 driver

From: Daniel Ribeiro <drwyrm-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
To: David Brownell <david-b-yBeKhBN/0LDR7s880joybQ@public.gmane.org>
Cc: Stefan Schmidt <stefan-4Bgg8jF3iZdg9hUCZPvPmw@public.gmane.org>,
	eric.y.miao-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	spi-devel-general-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org,
	sameo-RWuK6r/cQWRpLGFMi4vTTA@public.gmane.org,
	linux-arm-kernel-xIg/pKzrS19vn6HldHNs0ANdhmdF6hFW@public.gmane.org,
	Stefan Schmidt
	<stefan-OrPQZGeq07wqhVmZOOOmNx2eb7JE58TQ@public.gmane.org>
Subject: Re: [patch 05/14] mfd: PCAP2 driver
Date: Sun, 23 Nov 2008 05:06:02 -0200	[thread overview]
Message-ID: <1227423962.3148.74.camel@brutus> (raw)
In-Reply-To: <200811222059.59806.david-b-yBeKhBN/0LDR7s880joybQ@public.gmane.org>

Em Sáb, 2008-11-22 às 20:59 -0800, David Brownell escreveu:
> > I tried spi_write_then_read before, but it didn't work. I supposed it
> > was because it was doing 2 transfers as the second transfer rx_buf
> > always came zeroed.
> 
> You may have been using it wrong.  Also, verify against
> current kernels ... there have been bugfixes to pxa2xx_spi.
> 
> > I see that commit 
> > f9b90e39cbc5c4d6ef60022fd1f25d541df0aad1 changed it to do a single
> > transfer, so i will try it again.
> 
> Unless it needs the full duplex capability of SPI, then
> you should be able to make write_then_read work ... on
> the other hand, if you do need full duplex, then you
> should address the DMA.  (And byteswapping, either way.)

Well, i guess it is full duplex, as i set spi_transfer.len to 4 bytes,
write 4 bytes _and_ read 4 bytes to/from the chip.

I'm looking at write_then_read and if I read it correctly, it sends n_tx
bytes of data plus n_rx bytes of nothing, and discards n_tx bytes from
the start of the receive buffer considering only n_rx bytes from the end
of the receive buffer. This is not what i want.

Can you be more descriptive on "address the DMA"? Im not familiar on
what is the issue here.

I will take care of byte swapping for the next patch.

-- 
Daniel Ribeiro

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