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Message-ID: <dd5f6b9f-13bd-8127-71a8-40e7a7017d25@devtank.co.uk>
Date: Mon, 12 Aug 2019 22:03:32 +0100
From: Joe Burmeister <joe.burmeister@...tank.co.uk>
To: David Laight <David.Laight@...LAB.COM>,
Rob Herring <robh+dt@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Arnd Bergmann <arnd@...db.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
YueHaibing <yuehaibing@...wei.com>,
Bartosz Golaszewski <bgolaszewski@...libre.com>,
"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Add optional chip erase functionality to AT25 EEPROM
driver.
On 12/08/2019 16:51, David Laight wrote:
> From: Joe Burmeister
>> Sent: 09 August 2019 13:54
>>
>> 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".
> Is it actually worth doing though?
>
> I'm guessing that device erase can easily take over a minute.
That must depend on the AT25. The one we're using (AT25F512A), as it's
setup, it's fast enough. The datasheet states "The CHIP ERASE cycle time
typically is 2 seconds.". I've not timed it's because as I said, seamed
fast enough.
If you can't erase it, then it's basically write once, or you expose it
with spi_dev to Flashrom to erase it.
> When I looked at 'device erase' on an EEPROM it took just as long
> as erasing the sectors one at a time - but without the warm cosy
> feeling that progress was being made.
I didn't look at sector erase as I'm only interested in erasing it all
and there was a command for it. I figured if someone wanted sector by
sector they would implement it.
> Not only that you can't really interrupt the erase, so either
> the application has to sleep uninterruptibly for the duration
> or you have to have some kind of 'device busy' response while
> it is done asynchronously.
That's true, but as I said, it's fast enough it's not an issue for us.
> David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
Regards,
Joe
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