[U-Boot] spi-nor: Choices of choosing bank or 4-byte addressing

[U-Boot] spi-nor: Choices of choosing bank or 4-byte addressing

[Jagan Teki]

For accessing SPI-NOR flash's with > 16MiB we have two choices like
Bank/Extended and 4-byte addressing register support.

Status in u-boot:
1) BAR (Bank/Extended)
- Added support in u-boot already, tested

2) 4-byte addressing
- No support yet
- Hou Zhiqiang sent patches, those are review.

Ideally we may support any one of them, but there is some situation
where (q)spi controller can only support 3-byte addressing (not
supporting 4-byte addressing) but the connected flash could be >
16MiB, example: Xilinx Zynq QSPI

In this case as controller not supporting 4-byte commands we must use
BAR for accessing > 16MiB flash's.

Siva, suggested like from controller driver (spi_slave {} ) we need to
inform the flash about addressing width, so-that flash can configure
accordingly.

I indeed agree with this, and if we have both supported then the flash
will configure accordingly with controller check.

Pls- share for any other thoughts.

thanks!
-- 
Jagan | openedev.

[U-Boot] spi-nor: Choices of choosing bank or 4-byte addressing

[Marek Vasut]

On Monday, August 17, 2015 at 03:54:50 PM, Jagan Teki wrote:
> For accessing SPI-NOR flash's with > 16MiB we have two choices like
> Bank/Extended and 4-byte addressing register support.
> 
> Status in u-boot:
> 1) BAR (Bank/Extended)
> - Added support in u-boot already, tested
> 
> 2) 4-byte addressing
> - No support yet
> - Hou Zhiqiang sent patches, those are review.

Patchwork or gmane link would really help.

> Ideally we may support any one of them, but there is some situation
> where (q)spi controller can only support 3-byte addressing (not
> supporting 4-byte addressing) but the connected flash could be >
> 16MiB, example: Xilinx Zynq QSPI
> 
> In this case as controller not supporting 4-byte commands we must use
> BAR for accessing > 16MiB flash's.

So the controller in QSPI controller in Zynq is explicitly broken ?

> Siva, suggested like from controller driver (spi_slave {} ) we need to
> inform the flash about addressing width, so-that flash can configure
> accordingly.

Absolutelly not, you're mixing together SPI driver and a SPI NOR driver.

> I indeed agree with this, and if we have both supported then the flash
> will configure accordingly with controller check.
> 
> Pls- share for any other thoughts.
> 
> thanks!

Best regards,
Marek Vasut