linux-kernel - Re: [PATCH 1/4] media: dvb/af9015, implement eeprom hashing

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Message-ID: <4B5CDD4A.5060800@iki.fi>
Date:	Mon, 25 Jan 2010 01:52:42 +0200
From:	Antti Palosaari <crope@....fi>
To:	Jiri Slaby <jirislaby@...il.com>
CC:	Jiri Slaby <jslaby@...e.cz>, linux-kernel@...r.kernel.org,
	Mauro Carvalho Chehab <mchehab@...hat.com>,
	linux-media@...r.kernel.org
Subject: Re: [PATCH 1/4] media: dvb/af9015, implement eeprom hashing

On 01/24/2010 06:35 PM, Jiri Slaby wrote:
> On 01/24/2010 05:16 PM, Antti Palosaari wrote:
>>> +    af9015_config.eeprom_sum = 0;
>>> +    for (reg = 0; reg<   eeprom_size / sizeof(u32); reg++) {
>>> +        af9015_config.eeprom_sum *= GOLDEN_RATIO_PRIME_32;
>>> +        af9015_config.eeprom_sum += le32_to_cpu(((u32 *)eeprom)[reg]);
>>> +    }
>>> +
>>> +    deb_info("%s: eeprom sum=%.8x\n", __func__,
>>> af9015_config.eeprom_sum);
>>
>> Does this sum contain all 256 bytes from EEPROM? 256/4 is 64.
>
> Yes it does. It is computed as a hashed sum of 32-bit numbers (4 bytes)
> -- speed (does not matter) and larger space of hashes. Hence the
> division by 4. The cast does the trick: ((u32 *)eeprom)[reg] -- reg
> index is on a 4-byte basis.


OK, true. Anyhow, I don't know if this hashing formula is good enough - 
changing it later could be really pain. I compared it to the one used 
for em28xx driver and it was different. Could someone with better 
knowledge check that?

Generally it is good and ready for submission.

Acked-by: Antti Palosaari <crope@....fi>

regards
Antti
-- 
http://palosaari.fi/
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