[PATCH] ARM64: juno: add NOR flash to device tree

[sudeep.holla@arm.com (Sudeep Holla)]

On 18/10/15 10:25, Linus Walleij wrote:
> On Thu, Oct 15, 2015 at 5:30 PM, Sudeep Holla <sudeep.holla@arm.com> wrote:
>> Me
>>>   Results after
>>> enabling MTD, MTD_CFI, MTD_PHYSMAP, MTD_PHYSMAP_OF,
>>> MTD_CFI_INTELEXT:
>>
>> Just a note on this: we can't enable these when CPUIDLE is enabled as
>> the firmware assumes the flash is always in read mode while Linux leaves
>> NOR flash in "read id" mode after initialization.
>
> Sorry I'm too unfamiliar with this lingo. Can you give me some detail
> on what "read mode" and "read id" mode is all about?
>

OK, sorry for that I just quoted from my understanding. Here is the
actual one from the data sheet:

"The device can be in any of four read states: Read Array, Read
  Identifier, Read Status or Read Query. Upon power-up, or after a reset,
  the device defaults to Read Array. To change the read state, the
  appropriate read command must be written to the device..."

After the driver gets initialized, it usually leaves the device in Read
Identifier state as the last command sent is to read ID from the chip.

>> So until the firmware is ready to handle that, we can't enabled both
>> on Juno. We had same issue even on TC2. I will follow up internally to
>> see if we can fix on Juno at-least.
>
> Sounds like something that should be fixed for all Versatile
> Express that have cpuidle?
>

Correct, I just mentioned so that if you see/get any boot issue report
with NOR flash and CPUIdle enabled, you will have the background instead
of investigating the known issue again.

-- 
Regards,
Sudeep