Re: [PATCH] Add optional chip erase functionality to AT25 EEPROM driver.

[Joe Burmeister]

Hi Mark,


On 09/08/2019 14:54, Mark Rutland wrote:
> On Fri, Aug 09, 2019 at 01:53:55PM +0100, Joe Burmeister wrote:
> > Many, though not all, AT25s have an instruction for chip erase.
> > If there is one in the datasheet, it can be added to device tree.
> > Erase can then be done in userspace via the sysfs API with a new
> > "erase" device attribute. This matches the eeprom_93xx46 driver's
> > "erase".
> >
> > Signed-off-by: Joe Burmeister <joe.burmeister@xxxxxxxxxxxxx>
> > ---
> >   .../devicetree/bindings/eeprom/at25.txt       |  2 +
> >   drivers/misc/eeprom/at25.c                    | 83 ++++++++++++++++++-
> >   2 files changed, 82 insertions(+), 3 deletions(-)
> >
> > diff --git a/Documentation/devicetree/bindings/eeprom/at25.txt b/Documentation/devicetree/bindings/eeprom/at25.txt
> > index b3bde97dc199..c65d11e14c7a 100644
> > --- a/Documentation/devicetree/bindings/eeprom/at25.txt
> > +++ b/Documentation/devicetree/bindings/eeprom/at25.txt
> > @@ -19,6 +19,7 @@ Optional properties:
> >   - spi-cpha : SPI shifted clock phase, as per spi-bus bindings.
> >   - spi-cpol : SPI inverse clock polarity, as per spi-bus bindings.
> >   - read-only : this parameter-less property disables writes to the eeprom
> > +- chip_erase_instruction : Chip erase instruction for this AT25, often 0xc7 or 0x62.
> This should be using '-' rather than '_', as per general DT conventions
> and as with the existing properties.
>
> >   Obsolete legacy properties can be used in place of "size", "pagesize",
> >   "address-width", and "read-only":
> > @@ -39,4 +40,5 @@ Example:
> >   		pagesize = <64>;
> >   		size = <32768>;
> >   		address-width = <16>;
> > +		chip_erase_instruction = <0x62>;
> [...]
>
> > +	/* Optional chip erase instruction */
> > +	device_property_read_u8(&spi->dev, "chip_erase_instruction", &at25->erase_instr);
> This will not behave as you expect, since you didn't mark the property as
> 8-bits.

Rats, I forgot to update the documentation. In my device tree I have 
already found the /bit 8/ bit.

> Read this as a u32 into the existing val temporary variable, as is done
> for pagesize. You can add a warnign if it's out-of-range.

32bit would certainly read better in the device tree. I'll do that.

> Thanks,
> Mark.


Cheers,


Joe