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Date:	Thu, 10 Jul 2014 11:42:01 +0200
From:	Geert Uytterhoeven <>
To:	Harini Katakam <>
Cc:	Mark Brown <>,
	Grant Likely <>,
	Rob Herring <>,
	Pawel Moll <>,
	Mark Rutland <>,
	Ian Campbell <>,
	Kumar Gala <>,
	linux-spi <>,
	"" <>,
	"" <>,
	"" <>,
	David Woodhouse <>,
	Brian Norris <>,
	Marek VaĊĦut <>,
	Artem Bityutskiy <>,
	Geert Uytterhoeven <>,
	Sascha Hauer <>,
	Jingoo Han <>,
	Sourav Poddar <>,
	"" <>,
	Punnaiah Choudary Kalluri <>
Subject: Re: [RFC PATCH 1/2] spi: Add support for Zynq QSPI controller

Hi Harini,

On Thu, Jul 10, 2014 at 11:31 AM, Harini Katakam
<> wrote:
>>> +       master->mode_bits = SPI_CPOL | SPI_CPHA | SPI_RX_DUAL | SPI_RX_QUAD |
>>> +                           SPI_TX_DUAL | SPI_TX_QUAD;
>> Your driver advertises Dual/Quad SPI Transfer capabilities, but it doesn't
>> check spi_transfer.[tr]x_nbits? How can it determine when to enable Dual/Quad?
> Here the driver is just giving information that the controller support it.
> The MTD layer enables dual/quad based on what the flash supports; quad
> being the first priority
> I understand that the spi core reads rx, tx-bus-width property and
> master support flags and
> performs the necessary checks.

That's correct: as long as the rx, tx-bus-width  properties do not indicate a
Dual or Quad wiring, it won't be used.

However, based on schematics, someone may set the rx, tx-bus-width properties
to 4, which is correct, as DT describes the hardware. But this will fail to
So I think it's safer not to announce Dual/Quad support in the driver until
the actual driver support is there.



Geert Uytterhoeven -- There's lots of Linux beyond ia32 --

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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