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Subject: Re: [PATCH] Add optional chip erase functionality to AT25 EEPROM
 driver.
To:     Mark Rutland <mark.rutland@arm.com>
Cc:     Rob Herring <robh+dt@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
        YueHaibing <yuehaibing@huawei.com>,
        Bartosz Golaszewski <bgolaszewski@baylibre.com>,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20190809125358.24440-1-joe.burmeister@devtank.co.uk>
 <20190809135440.GI48423@lakrids.cambridge.arm.com>
From:   Joe Burmeister <joe.burmeister@devtank.co.uk>
Message-ID: <f9316727-607b-7c05-1c47-05319b3cdecf@devtank.co.uk>
Date:   Fri, 9 Aug 2019 17:28:42 +0100
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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@devtank.co.uk>
>> ---
>>   .../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