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

[Roger Quadros <rogerq@ti.com>]

On 08/01/2014 09:38 AM, Tony Lindgren wrote:
> * 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.

It is more like a board configuration so something more generic than the gpmc driver has to manage.
Also, QSPI and MMC don't fall under GPMC scope.

There are 2 things that need to change to update the hardware configuration.
1) The pinmux via the enabling/disabling (or plugging in/out) of relevant nodes in the DT.
2) The I2C GPIOs which reconfigure the DIP Switch lines in order to reconfigure external Muxes.

cheers,
-roger