linux-kernel - Re: [PATCH 2/3] iio: temperature: add max6675 thermocouple converter driver

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sat, 8 Aug 2015 12:39:40 +0100
From:	Jonathan Cameron <jic23@...nel.org>
To:	Matt Porter <mporter@...sulko.com>,
	Peter Meerwald <pmeerw@...erw.net>
Cc:	Linux IIO List <linux-iio@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] iio: temperature: add max6675 thermocouple converter
 driver

On 06/08/15 18:38, Matt Porter wrote:
> On Mon, Aug 03, 2015 at 11:26:12PM +0200, Peter Meerwald wrote:
>> On Mon, 3 Aug 2015, Matt Porter wrote:
> 
> ...
> 
>>> +static int max6675_read(struct max6675_state *st, int *val)
>>> +{
>>> +	int ret;
>>> +
>>> +	ret = spi_read(st->spi, val, 2);
>>> +	if (ret < 0)
>>> +		return ret;
>>> +
>>> +	/* Temperature is bits 14..3 */
>>> +	*val = (*val >> 3) & 0xfff;
>>
>> what about endianness conversion?
>> use be16_to_cpu()
> 
> Apologies, I spoke before engaging the brain on my first reply to this
> As specified by the SPI subsystem docs, SPI buffers are always stored
> in native endian order. There is no need for endianness conversion here.
First of all, which doc say this?
Secondly how does SPI know the endianness of the sensor which is what
actually matters here?  I2C can in theory make these guarantees as there
is an expected byte order on the wire (even if quite a few drivers don't
conform to the spec anyway). No such guarantee can exist for SPI.

Jonathan


> 
> -Matt
> --
> To unsubscribe from this list: send the line "unsubscribe linux-iio" in
> the body of a message to majordomo@...r.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/