linux-kernel - Re: [PATCH 1/3] soundwire: remove bitfield for unique

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Message-ID: <20191024112955.GC2620@vkoul-mobl>
Date:   Thu, 24 Oct 2019 16:59:55 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
Cc:     alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        tiwai@...e.de, broonie@...nel.org, gregkh@...uxfoundation.org,
        jank@...ence.com, srinivas.kandagatla@...aro.org,
        slawomir.blauciak@...el.com,
        Bard liao <yung-chuan.liao@...ux.intel.com>,
        Rander Wang <rander.wang@...ux.intel.com>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        Sanyog Kale <sanyog.r.kale@...el.com>
Subject: Re: [PATCH 1/3] soundwire: remove bitfield for unique_id, use u8

On 22-10-19, 18:48, Pierre-Louis Bossart wrote:
> There is no good reason why the unique_id needs to be stored as 4
> bits. The code will work without changes with a u8 since all values

Well this was due to the fact the slave id defined by MIPI has unique id
as 4 bits. In fact if you look closely there are other fields in
sdw_slave_id doing this

> are already filtered while parsing the ACPI tables and Slave devID
> registers.
> 
> Use u8 representation. This will allow us to encode a
> "IGNORE_UNIQUE_ID" value to account for firmware/BIOS creativity.

Why are we shoving firmware/BIOS issues into the core?

> 
> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
> ---
>  include/linux/soundwire/sdw.h | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/soundwire/sdw.h b/include/linux/soundwire/sdw.h
> index 688b40e65c89..28745b9ba279 100644
> --- a/include/linux/soundwire/sdw.h
> +++ b/include/linux/soundwire/sdw.h
> @@ -403,6 +403,8 @@ int sdw_slave_read_prop(struct sdw_slave *slave);
>   * SDW Slave Structures and APIs
>   */
>  
> +#define SDW_IGNORED_UNIQUE_ID 0xFF
> +
>  /**
>   * struct sdw_slave_id - Slave ID
>   * @mfg_id: MIPI Manufacturer ID
> @@ -418,7 +420,7 @@ struct sdw_slave_id {
>  	__u16 mfg_id;
>  	__u16 part_id;
>  	__u8 class_id;
> -	__u8 unique_id:4;
> +	__u8 unique_id;
>  	__u8 sdw_version:4;
>  };
>  
> -- 
> 2.20.1

-- 
~Vinod