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

[Harini Katakam <harinikatakamlinux@xxxxxxxxx>]

Hi Geert,

On Thu, Jul 10, 2014 at 3:12 PM, Geert Uytterhoeven
<geert@xxxxxxxxxxxxxx> wrote:
> Hi Harini,
>
> On Thu, Jul 10, 2014 at 11:31 AM, Harini Katakam
> <harinikatakamlinux@xxxxxxxxx> 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.
>

OK. Correct me if I'm wrong but announcing this support in master->flags is
just to say the controller supports it - Like Punnaiah mentioned in the other
mail, nothing specific needs to be done from the controller driver to enable
dual/quad support. This is at the SOC/IP level.
I agree it might or might not be supported at board-level.
But that's based on the user's hardware. Should master->flags
really take this into consideration?

BTW, I dint see master->mode_bits being used anywhere at the moment.

Regards,
Harini
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