On 20 November 2015 at 19:13, Simon Falsig <si...@newtec.dk> wrote:
> I have a custom board based on a TI AM3356 processor (quite similar to
> a BeagleBone) with an Everspin MR25H256 MRAM attached to the SPI bus,
> currently using U-Boot 2015.10 to boot a 3.18.9-rt5 Linux kernel.
>
> I'd like to use this MRAM to store the MAC address for one of the
> Ethernet interfaces, but I'm having a bit of trouble getting started
> on how support for this should be added.
>
> I can access the MRAM just fine from Linux (using the m25p80 driver
> and the MTD framework), so with the appropriate drivers compiled into
> the kernel, Linux picks the chip up without any issue by simply adding
> the following to the device tree:
>
> mram: m25p80@0 {
> #address-cells = <1>;
> #size-cells = <1>;
> compatible = "mr25h256";
> reg = <0>;
> spi-max-frequency = <40000000>;
> status = "okay";
> };
>
> I'd like U-Boot to do something similar, but there are a few issues:
> 1. The chip is not JEDEC compatible, so it cannot be probed like
> the other chips currently listed in drivers/mtd/spi/sf_params.c
> 2. Since it's an MRAM, it doesn't need to be erased before being
> written - Linux has a flag for this, but it doesn't seem as if
> U-Boot has anything similar. (Not that I need this currently
> though, as I only need to be able to read the chip for now - but
> it'd be nice to have, and others might be able to use it too.)
>
Thanks for your concerns, It's been very clear.
> I've tried having a look at doc/driver-model/spi-howto.txt, hoping
> that this would have up-to-date information on how to implement/modify
> a SPI driver, but when I for instance look at spi_setup_slave_fdt(),
> which seems to be one of the necessary functions, I can only find it
> implemented in drivers/spi/spi-uclass.c, with a comment saying that
> it is only for compatibility, and that it is to be removed?...
These are spi drivers not related to spi-flash.
drivers/mtd/spi/sf_probe.c
drivers/mtd/spi/sf_ops.c are spi-flash related.
If possible you can add non-jedec things to sf_probe.c similar way as
Linux, BTW I'm currently working spi-flash subsystem which should as
modular as Linux[1]. I hope we may get that version coming releases,
but what ever is feasible to you just work on that I would help you
always.
>
> If anyone can help me with a few hints on how to get started adding
> support for this chip, it'd be much appreciated!
>
> Thanks in advance and best regards,
[1]
http://git.denx.de/?p=u-boot/u-boot-spi.git;a=shortlog;h=refs/heads/spi-nor-mtd
--
Jagan | openedev.
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