Re: [PATCH] gpio: pca953x: Use correct u16 value for register word write
From: Yong Li
Date: Wed Mar 30 2016 - 01:01:42 EST
Or another method is using the below to convert the u8 to u16:
cpu_to_le16(get_unaligned((u16 *) val)), compared with the
i2c_smbus_write_byte_data method, which one is better?
2016-03-30 10:43 GMT+08:00 Yong Li <sdliyong@xxxxxxxxx>:
> If use the get_unaligned, below is the code example, but we cannot detect if
> it is big endian or little endian. I would like to use the same write logic
> as PCA957X_TYPE: use the i2c_smbus_write_byte_data API to write two times.
> How do you think about it?
> if (big_endian)
> value = get_unaligned_be16(buf);
> value = get_unaligned_le16(buf);
> Yong Li
> 2016-03-30 0:33 GMT+08:00 Phil Reid <preid@xxxxxxxxxxxxxxxxx>:
>> On 29/03/2016 10:39 PM, Alexander Stein wrote:
>>> You missed CC'ing Phil (Added for this post)
>>> On Tuesday 29 March 2016 20:53:58, Yong Li wrote:
>>>> Thanks for your comment, I think I can change it to val | (val
>>>> << 8), is it okay ?
>>> Mh, currently there is only one caller (device_pca953x_init) which passes
>>> 0, 0 or 0xff, 0xff, so endianess is irrelevant. But to be future proof
>>> should be done in an endian-safe manner. Though cpu_to_le16p does not
>>> due to same alignment problem as casting to u16*.
>> I think get_unaligned((u16 *) val) should do the job.
>> There's also get_unaligned_le* get_unaligned_be*
>> Phil Reid