linux-kernel - Re: [RFC PATCH 1/2] spi: Add support for Zynq QSPI controller

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Date:	Thu, 10 Jul 2014 11:42:01 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Harini Katakam <harinikatakamlinux@...il.com>
Cc:	Mark Brown <broonie@...nel.org>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	linux-spi <linux-spi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	Marek Vašut <marex@...x.de>,
	Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>,
	Geert Uytterhoeven <geert+renesas@...ux-m68k.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Jingoo Han <jg1.han@...sung.com>,
	Sourav Poddar <sourav.poddar@...com>,
	"michals@...inx.com" <michals@...inx.com>,
	Punnaiah Choudary Kalluri <punnaia@...inx.com>
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
<harinikatakamlinux@...il.com> 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
work.
So I think it's safer not to announce Dual/Quad support in the driver until
the actual driver support is there.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

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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