linux-kernel - Re: [alsa-devel] [RFC PATCH 24/40] soundwire: cadence_master: use BIOS defaults for frame shape

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Date:   Fri, 26 Jul 2019 09:22:21 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Cezary Rojewski <cezary.rojewski@...el.com>
Cc:     alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        tiwai@...e.de, broonie@...nel.org, vkoul@...nel.org,
        gregkh@...uxfoundation.org, jank@...ence.com,
        srinivas.kandagatla@...aro.org, slawomir.blauciak@...el.com,
        Sanyog Kale <sanyog.r.kale@...el.com>
Subject: Re: [alsa-devel] [RFC PATCH 24/40] soundwire: cadence_master: use
 BIOS defaults for frame shape



On 7/26/19 5:20 AM, Cezary Rojewski wrote:
> On 2019-07-26 01:40, Pierre-Louis Bossart wrote:
>> +static u32 cdns_set_default_frame_shape(int n_rows, int n_cols)
>> +{
>> +    u32 val;
>> +    int c;
>> +    int r;
>> +
>> +    r = sdw_find_row_index(n_rows);
>> +    c = sdw_find_col_index(n_cols);
>> +
>> +    val = (r << 3) | c;
>> +
>> +    return val;
>> +}
>> +
>>   /**
>>    * sdw_cdns_init() - Cadence initialization
>>    * @cdns: Cadence instance
>> @@ -977,7 +990,9 @@ int sdw_cdns_init(struct sdw_cdns *cdns)
>>       cdns_writel(cdns, CDNS_MCP_CLK_CTRL0, val);
>>       /* Set the default frame shape */
>> -    cdns_writel(cdns, CDNS_MCP_FRAME_SHAPE_INIT, 
>> CDNS_DEFAULT_FRAME_SHAPE);
>> +    val = cdns_set_default_frame_shape(prop->default_row,
>> +                       prop->default_col);
>> +    cdns_writel(cdns, CDNS_MCP_FRAME_SHAPE_INIT, val);
>>       /* Set SSP interval to default value */
>>       cdns_writel(cdns, CDNS_MCP_SSP_CTRL0, CDNS_DEFAULT_SSP_INTERVAL);
>>
> 
> Suggestion:
> declare "generic" _get_frame_frame(rows, cols) instead and let it do the 
> bitwise operations for you. Pretty sure this won't be the only place in 
> code where reg value for frame_shape needs to be prepared.
> 
> Said function could be as simple as:
> return (row << 3) | cols;
> +inline flag
> 
> i.e. could be even a macro..
> 
> Otherwise modify _set_default_frame_shape to simply:
> return (r << 3) | c
> 
> without involving additional local val variable (I don't really see the 
> point for any locals there though).

what this function does is take the standard-defined offsets for row and 
column and stores them in a Cadence-defined register. I think we can 
probably use a macro to remove the magic '3' value, but there are limits 
to what we can simplify. I should probably add comments so that people 
figure it out.