Hi Bill,

On Wed, 26 Aug 2015 11:26:36 -0400
Bill Pringlemeir [off-list ref] wrote:

On 25 Aug 2015, computersforpeace-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org wrote:

quoted

Sorry, I realized a potential issue here.

quoted

On Mon, Aug 03, 2015 at 11:27:28AM +0200, Stefan Agner wrote:

quoted

Signed-off-by: Bill Pringlemeir <redacted>
Acked-by: Shawn Guo <redacted>
Reviewed-by: Brian Norris <redacted>
Signed-off-by: Stefan Agner <redacted>
---
.../devicetree/bindings/mtd/vf610-nfc.txt | 45 ++++++++++++++++++++++
1 file changed, 45 insertions(+) create mode 100644
Documentation/devicetree/bindings/mtd/vf610-nfc.txt

quoted

quoted

diff --git a/Documentation/devicetree/bindings/mtd/vf610-nfc.txt

b/Documentation/devicetree/bindings/mtd/vf610-nfc.txt
new file mode 100644
index 0000000..cae5f25

--- /dev/null
+++ b/Documentation/devicetree/bindings/mtd/vf610-nfc.txt

quoted

quoted

-0,0 +1,45 @@

+- nand-bus-width: see nand.txt
+- nand-ecc-mode: see nand.txt
+- nand-on-flash-bbt: see nand.txt

quoted

Stumbling across the "multi-CS" questions on the driver reminds me: it
typically makes sense to define new NAND bindings using separate NAND
*controller* and *flash* device nodes. The above 3 properties, at
least, would apply on a per-flash basis, not per-controller
typically. See sunxi-nand, for instance:

quoted

http://lxr.free-electrons.com/source/Documentation/devicetree/bindings/mtd/sunxi-nand.txt

quoted

brcmnand had a similar pattern:

quoted

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/mtd/brcm,brcmnand.txt

quoted

(Perhaps it's time we standardized this a little more formally...)

These would apply per chip, but the controller has to be configured to
support each and every one.  Every time an operation was performed, we
would have to check the chip type and reconfigure the controller.
Currently, the driver does not support this and it would add a lot of
overhead in some cases unless a register cache was used.

Is the flexibility of using a system with combined 8/16bit devices
really worth all the overhead?  Isn't it sort of brain dead hardware not
to make all of the chips similar?  Why would everyone have to pay for
such a crazy setup?

To separate it would at least be a lie versus the code in the current
form.  As well, there are only a few SOC which support multiple chip
selects.  The 'multi-CS' register bits of this controller varies between
PowerPC, 68K/Coldfire and ARM platforms.

I looked briefly at the brcmnand.c  and it seems that it is not
supporting different ECC per chip even though the nodes are broken out
this way.  In fact, if some raw functions are called, I think it will
put it in ECC mode even if it wasn't before?  Well, I agree that this
would be good generically, I think it puts a lot of effort in the
drivers for not so much payoff?

Hm, the sunxi driver supports it, and it does not add such a big
overhead...
The only thing you have to do is cache a bunch of register values
per-chip and restore/apply them when the chip is selected
(in your ->select_chip() implementation).

Anyway, even if the suggested DT representation is a lie in regards to
your implementation, it's actually pretty accurate from an hardware
POV, and this is exactly what DT is supposed to represent.

Best Regards,

Boris

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html