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Subject: Re: Add --skip-all-ffs option to mtd-utils nandwrite
To: David Oberhollenzer <david.oberhollenzer@sigma-star.at>,
 Kees Trommel <ctrommel@aimvalley.nl>, linux-mtd@lists.infradead.org
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From: Marek Vasut <marek.vasut@gmail.com>
Message-ID: <d4a1082b-d79a-8c90-b17d-5d559e32308a@gmail.com>
Date: Wed, 7 Dec 2016 15:09:49 +0100
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On 12/07/2016 09:21 AM, David Oberhollenzer wrote:
> On 12/07/2016 06:01 AM, Marek Vasut wrote:
>> +               if (skipallffs)
>> +               {
>> +                       for (ii = 0; ii < mtd.min_io_size; ii +=
>> sizeof(uint32_t))
>> +                       {
>> +                               if (*(uint32_t*)(writebuf + ii) !=
>> 0xffffffff)
>> +                                       break;
>>
>> Is this memcmp()-alike function ?
>>
>> +                       }
>> +                       if (ii == mtd.min_io_size)
>> +                               allffs = 1;
>> +               }
>> +               if (!allffs) {
> The point of the patch is not to write a page that is filled with 0xFF bytes.
> A feature that is turned off by default and can be activated via a command
> line switch.

That much I figured out

> The code you are trying to replace tries to figure out if an entire block of
> memory is set to 0xFF. The code path should be conditional, as this feature
> is turned off unless explicitly requested.

And to do that, we need to open-code it like above ?
Looks pretty crappy.

>> This could be simply turned to:
>>
>> ret = 0;
>> if (!memcmp(writebuf, writebuf + 1, mtd.min_io_size - 1)) {
>>     ret = mtd_write(....);
>> }
> This does something completely different.

It checks whether the buffer if full of the same bytes, yes ?
Add additional conditions as needed (check whether user provided
the arg and whether byte 0 in the buffer is 0xff and you should
be done).

-- 
Best regards,
Marek Vasut