[BUG]: spi-nor: spi_nor_init() fails when SR locked

[Tudor.Ambarus at microchip.com]

Hi, David,

On 7/20/20 9:13 PM, David Clear wrote:
> 
> Hi Tudor,
> 
> I'm seeing a change of behavior in spi-nor/next vs. my older 4.14
> kernel w.r.t. how SR lock is working.
> 
> In my system with a Micron mt25qu02g, I'm using the hardware WP# to
> lock the SR.  When hardware write-protect is on, at the next reboot
> the kernel rejects the flash as it cannot unlock the whole device.
> 
> I traced the problem to spi_nor_write_sr1_and_check(), which is
> writing to the SR and reading back a different value (as the locked SR
> bits are immutable).
> 
> Call trace:
>  spi_nor_write_sr1_and_check+0x68/0x70
>  spi_nor_write_sr_and_check+0x34/0xd0
>  spi_nor_sr_unlock+0x108/0x230
>  spi_nor_unlock+0x54/0x80  (via spi_nor_unlock_all())
>  spi_nor_init+0x94/0x100
> 
> spi_nor_write_sr1_and_check() is returning -EIO here:
>         if (nor->bouncebuf[0] != sr1) {
>                 dev_dbg(nor->dev, "SR1: read back test failed\n");
>                 BUG();
>                 return -EIO;
>         }
> 
> In my specific case Linux doesn't have (and cannot be given, for
> product security reasons) control over the WP#.  In any case, I don't
> think a write-protected flash should be rejected here.
> 
> Can you suggest how we might proceed?  The way WP# is used is
> board-specific so perhaps a device-tree property of some sort in the
> flash device node can inform the code to do or not do the
> spi_nor_unlock_all()?
> 
> I can take a look at putting a patch together if you suggest an
> acceptable mechanism.
> 

Thanks for the detailed report. I'll have to study this a bit, I'll get
back to you in few days/one week. We tackled the unlock_all stuff in
the past, Michael did a patch, I'll check how that fits here.

https://patchwork.ozlabs.org/project/linux-mtd/patch/20200327155939.13153-1-michael@walle.cc/

Cheers,
ta