linux-kernel - Re: [PATCH] eeprom: at25: set minimum read/write access stride to 1

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Date:   Tue, 28 Jul 2020 14:03:30 +0200
From:   Christian Eggers <ceggers@...i.de>
To:     David Laight <David.Laight@...lab.com>
CC:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] eeprom: at25: set minimum read/write access stride to 1

On Tuesday, 28 July 2020, 13:20:15 CEST, David Laight wrote:
> From: Christian Eggers
> 
> > &spi {
> >     ....
> >     fram: fram@0 {
> >     ...
> >         mac_address_fec2: mac-address@126 {
> >             reg = <0x126 6>;
> >         };
> >     ...
> >     };
> > };
> 
> 
> Hmmmm.... the 'stride' only constrains the alignment of 'cells'.
> (ie address ranges from the device tree.)

My mac-address is not aligned to 4 bytes...

> It looks as though you can open the entire NVMEM device and
> then do reads from byte offsets.
> The 'stride' and 'word_size' are then not checked!

When I set back the stride to 4, I get the following errors:
[    6.998788] 000: nvmem spi0.00: cell mac-address unaligned to nvmem stride 4
[    6.998902] 000: at25: probe of spi0.0 failed with error -22
...
[    7.146454] 000: fec 20b4000.ethernet: Invalid MAC address: 00:00:00:00:00:00
[    7.146480] 000: fec 20b4000.ethernet: Using random MAC address: 6e:9d:37:49:6d:15

> Actually it might be that before 01973a01f9ec3 byte aligned
> 'cells' were allowed.

I use linux-5.4.x (latest), the mentioned patch has been included long time ago.

regards
Christian