Re: [PATCH] ARM: dts: dra7-evm: add parallel NOR flash support

[Tony Lindgren <tony@atomide.com>]

* Roger Quadros <rogerq@ti.com> [140731 04:46]:
> +Sourav for QSPI and Balaji for mmc
> 
> On 07/30/2014 10:40 PM, Pekon Gupta wrote:
> > Hi Roger,
> > 
> > On Tue, Jul 29, 2014 at 5:45 PM, Roger Quadros <rogerq@ti.com> wrote:
> >> On 07/23/2014 01:58 PM, Pekon Gupta wrote:
> >>> This patch adds support for parallel NOR device (S29GL512S10) present on J6-EVM.
> >>> The Flash device is connected to GPMC controller on chip-select[0] and accessed
> >>> as memory-mapped device. It has data-witdh=x16, capacity-64MBytes(512Mbits) and
> >>> is CFI compatible.
> >>> As multiple devices are share GPMC pins on this board, so following board
> >>> settings are required to detect NOR device:
> >>>      SW5.1 (NAND_BOOTn) = OFF (logic-1)
> >>>      SW5.2 (NOR_BOOTn)  = ON  (logic-0) /* Active-low */
> >>>      SW5.3 (eMMC_BOOTn) = OFF (logic-1)
> >>>      SW5.4 (QSPI_BOOTn) = OFF (logic-1)
> >>
> >> Why does NOR have any dependency on states of eMMC_BOOTn and QSPI_BOOTn?
> >>
> > If you see the schematics of J6-EVM, GPMC data and control lines are shared
> > between NAND, NOR, eMMC (and probably QSPI also).
> > I don't have access to TI's hardaware or board schematics anymore, so
> > please double check.
> 
> I just took a deeper look in the schematics.
> It has nothing to do with GPMC Data and control lines but with the address lines.
> The GPMC address lines are muxed on the same pins of the SoC as QSPI and MMC2.
> i.e. A13-A18,CS2 for QSPI and A19-A27,CS1 for MMC2
> 
> NAND can probably work simultaneously with QSPI and MMC2 but for NOR case, QSPI and MMC2
> need to be disabled.
> 
> This is starting to look ugly where apart from changing the DIP switch the DTS has to be
> hand modified to support a certain case.
> 
> Lets leave the most usable configuration for default case i.e. NAND, QSPI and MMC2 enabled and keep NOR information in the dts but keep it disabled with a note that if NOR is enabled then NAND, QSPI, and MMC2 nodes need to be disabled.
> 
> I will resend this patch with the relevant changes.

It might make sense for the gpmc driver to manage the pins in some
cases. That would allow dynamic muxing of the pins depending which
driver is loaded, or even during runtime if needed.

Regards,

Tony