[U-Boot] [PATCH v2 2/2] mtd: add altera quadspi driver

Jagan Teki
2015-11-06T08:07:21Z

Hi Thomas,

On 6 November 2015 at 05:48, Thomas Chou <thomas@wytron.com.tw> wrote:
> Hi Jagan,
>
> On 2015?11?05? 22:57, Jagan Teki wrote:
>>
>> The altera quad spi core is very special that the hardware handle the
>>>
>>> spi-nor protocol. The core is designed to replace the CFI flash
>>> interface.
>>> So there is nothing to do with SPI from the parallel flash interface. It
>>> is
>>> memory mapped. There is no SPI interface. There is nothing related to SPI
>>> programming. So please don't worry about the progress on spi-nor. The
>>> core
>>> should belong to parallel flash, but not serial flash.
>>
>>
>> Agreed that this is not doing any generic spi things, but it's a
>> spi-nor controller all spi-nor controller should be part of spi-nor
>> subsystem Linux agreed and have a framework for that.
>>
>> drivers/mtd/spi-nor/fsl-quadspi.c
>> drivers/mtd/spi-nor/nxp-spifi.c
>>
>> all these are spi-nor controller which doesn't do any generic spi
>> things but should be in spi-nor subsystem. Even Marek send altera_qspi
>> as spi-nor controller [1]
>>
>> Since I'm working on similar spi-nor subsystem what Linux have +
>> driver model little worried about this because once we have spi-nor
>> again it should be a re-work.
>>
>> [1] http://lists.infradead.org/pipermail/linux-mtd/2015-April/058650.html
>
>
> I had been a hardware engineer. I designed chips and boards. I believe this
> should depend on the programming interface. Eg, there are SSDs of SATA
> interfaces which build with NAND or EMMC, and it dose not make sense to
> classify them as NAND or MMC. The altera quadspi core is a similar case,
> because the hardware converts the programming interface. There is no way to
> send spi-nor commands that the spi frame work does. It is ridiculous to
> insist it to use under the spi-nor framework.

I appreciate your hardware expertise and am not questioning about that
as well. I do agree with the hw logic about altera qspi controller and
I don't have any questions with hw either.

But my main intention here was about the software support since Linux
discussed about this subject and finally moved to spi-nor controllers
(though they don't use spi bus at-all) to spi-nor framework and Marek
knows this topic very well.

I believe discussion about this topic much more clear if we send this
driver to Linux.

>
> The altera quadspi hides details about the underlying spi-nor. We may even
> choose to build interface that convert EMMC to like cfi flash. The users can
> run code directly on the flash or use memory command like "cp.b" of u-boot
> to program the flash. This can be a advantage over the "sf" command.

thanks!
--
Jagan | openedev.