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Subject: Re: [RFC PATCH] mtd: spi-nor: add support to non-uniform SPI NOR
 flash memories
To:     Tudor Ambarus <tudor.ambarus@microchip.com>,
        cyrille.pitchen@microchip.com, dwmw2@infradead.org,
        computersforpeace@gmail.com, boris.brezillon@bootlin.com,
        richard@nod.at
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        nicolas.ferre@microchip.com, Cristian.Birsan@microchip.com
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From:   Marek Vasut <marek.vasut@gmail.com>
Message-ID: <aa083709-c3e2-f075-1a99-c31399a1cb77@gmail.com>
Date:   Wed, 23 May 2018 14:54:17 +0200
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On 05/23/2018 02:52 PM, Tudor Ambarus wrote:
> Hi, Marek,

Hi,

> On 05/23/2018 12:56 PM, Marek Vasut wrote:
> [...]
>>>> [...]
>>>>
>>>>>>> +    while (len) {
>>>>>>> +        cmd = spi_nor_find_best_erase_cmd(map, region, addr, len);
>>>>>>> +        if (!cmd)
>>>>>>> +            return -EINVAL;
>>>>>> What would happen if you realize mid-way that you cannot erase some
>>>>>> sector , do you end up with partial erase ?
>>>>> Is this possible? In non-overlaid regions, the address is aligned with
>>>>> at least one of the erase commands, else -EINVAL. For overlaid regions
>>>>> alignment doesn't matter. But yes, if this is possible, in this case,
>>>>> this proposal will do a partial erase.
>>>> Shouldn't we fail up front instead ?
>>> It will be great if we can do this without having performance penalties.
>>> Can we loose the conditions for the last erase command? If one wants to
>>> erase 80k chunk starting from offset 0 and only 32k and 64k erase type
>>> are supported, can we erase 96k?
>> No. But can you maybe build a list of erase commands to be executed once
>> you validate that the erase can be performed for example ?
> 
> My second choice was an array witch saves u8 opcode and u32 erasesize.
> There are flashes of 256MB, in the worst case scenario with 4k erase
> type, we will end up with 64K entries.

Some RLE encoding might help here ?

> How about enforcing the length to be multiple of mtd->erasesize, like we
> do in uniform_erase? With this, the problem disappears.

What is the erase size for the 4k-sector 256MiB flash ?

-- 
Best regards,
Marek Vasut