From mboxrd@z Thu Jan  1 00:00:00 1970
From: Guenter Roeck <guenter.roeck@ericsson.com>
Date: Tue, 15 Feb 2011 01:23:52 +0000
Subject: Re: [lm-sensors] [PATCH] sensors-detect: DDR3 SPD EEPROM support
Message-Id: <20110215012352.GA28194@ericsson.com>
List-Id: <lm-sensors.vger.kernel.org>
References: <4D54FC00.1010600@ladisch.de>
In-Reply-To: <4D54FC00.1010600@ladisch.de>
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To: lm-sensors@vger.kernel.org

On Fri, Feb 11, 2011 at 04:06:08AM -0500, Clemens Ladisch wrote:
> This adds CRC-16 calculation, needed to correctly detect DDR3 SPD EEPROMs.
> 
For DDR3: Tested-by: Guenter Roeck <guenter.roeck@ericsson.com>

> --- a/prog/detect/sensors-detect
> +++ b/prog/detect/sensors-detect
> @@ -5265,18 +5265,43 @@
>  
>  # Registers used:
>  #   0-63: SPD Data and Checksum
> +#   0-127: SPD data and CRC (DDR3)
>  sub eeprom_detect
>  {
>  	my ($file, $addr) = @_;
> +	my $device_type = i2c_smbus_read_byte_data($file, 2);
>  	my $checksum = 0;
>  
>  	# Check the checksum for validity (works for most DIMMs and RIMMs)
> -	for (my $i = 0; $i <= 62; $i++) {
> -		$checksum += i2c_smbus_read_byte_data($file, $i);
> +	if ($device_type >= 1 and $device_type <= 10) {
> +		for (my $i = 0; $i <= 62; $i++) {
> +			$checksum += i2c_smbus_read_byte_data($file, $i);
> +		}
> +		$checksum &= 255;
> +
> +		return 8 if $checksum = i2c_smbus_read_byte_data($file, 63);
> +	} elsif ($device_type = 11) {
> +		# see JEDEC 21-C 4.1.2.11 2.4
> +		my $crc_coverage = i2c_smbus_read_byte_data($file, 0);
> +		$crc_coverage = ($crc_coverage & 0x80) ? 117 : 126;
> +		for (my $i = 0; $i < $crc_coverage; $i++) {
> +			$checksum ^= i2c_smbus_read_byte_data($file, $i) << 8;
> +			for (my $bit = 0; $bit < 8; $bit++) {
> +				if ($checksum & 0x8000) {
> +					$checksum = ($checksum << 1) ^ 0x1021;
> +				} else {
> +					$checksum <<= 1;
> +				}
> +			}
> +		}
> +		$checksum &= 0xffff;
> +
> +		return 8 if ($checksum & 0xff) = i2c_smbus_read_byte_data($file, 126) and
> +			    ($checksum >> 8) = i2c_smbus_read_byte_data($file, 127);
> +
> +		# note: if bit 7 of byte 32 is set, a jc42 sensor is at $addr-0x38
>  	}
> -	$checksum &= 255;
>  
> -	return 8 if $checksum = i2c_smbus_read_byte_data($file, 63);
>  	return;
>  }
>  
> 
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