On Thursday 09 January 2014 08:14 PM, Geert Uytterhoeven wrote:
CC linux-spi, and more information below.
On Thu, Jan 9, 2014 at 10:12 AM, Geert Uytterhoeven
<[email protected]> wrote:
Hi Sourav, Brian,
I'm working on adding QSPI support to a SPI master driver, so I'm very
interested in your work to add quad read support to m25p80.
Thanks for that!
However, I have a few questions/comments:
1. Up to version 2 of "drivers: mtd: m25p80: Add quad read support",
the driver set rx_nbits to indicate it wants to use Quad SPI transfers:
+ t[1].rx_nbits = flash->quad_read ? SPI_NBITS_QUAD : 1;
(http://patchwork.ozlabs.org/patch/286109/).
However, this is not present in later versions, nor in the current version
in -next.
May be, but I suppose all the quad related patches are pushed to l2-mtd.
You can
check it in that branch.
It's my understanding the default (single transfer mode) will be used if
rx_nbits is zero, cfr. drivers/spi/spi.c:__spi_async():
if (xfer->tx_buf&& !xfer->tx_nbits)
xfer->tx_nbits = SPI_NBITS_SINGLE;
if (xfer->rx_buf&& !xfer->rx_nbits)
xfer->rx_nbits = SPI_NBITS_SINGLE;
Does it really use quad transfers without setting rx_nbits to SPI_NBITS_QUAD?
I can confirm that the SPI master driver is called with rx_nbits == 1, while
using the 0x6b QOR command.
2. IMHO checking for Quad support in the SPI master (master->mode_bits)
and in the SPI FLASH chip is not sufficient. A quad-capable SPI FLASH
may be wired to a quad-capable SPI master using 4-wire mode, either
physically or through pin control.
So I think we need a m25p,quad-read property in DT.
We need the following to support quad,
1. controller side support -- > spi->mode should be set
2. flash support ---> provided as a flag.
3. Individuall transfer set --> done by t. rx/tx_nbits.
Sorry, this issue is moot. I missed that spi_device.mode (as set from DT
spi-rx-bus-width and spi-tx-bus-width) is also taken into account.
Thanks again!
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected]
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
--
To unsubscribe from this list: send the line "unsubscribe linux-spi" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
