linux-kernel - Re: [alsa-devel] [PATCH 06/17] soundwire: cadence_master: use firmware defaults for frame shape

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Date:   Tue, 6 Aug 2019 10:36:32 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Cezary Rojewski <cezary.rojewski@...el.com>
Cc:     alsa-devel@...a-project.org, Blauciak@...r.kernel.org,
        tiwai@...e.de, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, vkoul@...nel.org, broonie@...nel.org,
        srinivas.kandagatla@...aro.org, jank@...ence.com,
        Slawomir <slawomir.blauciak@...el.com>,
        Sanyog Kale <sanyog.r.kale@...el.com>
Subject: Re: [alsa-devel] [PATCH 06/17] soundwire: cadence_master: use
 firmware defaults for frame shape



On 8/6/19 10:27 AM, Cezary Rojewski wrote:
> On 2019-08-06 02:55, Pierre-Louis Bossart wrote:
>> diff --git a/drivers/soundwire/cadence_master.c 
>> b/drivers/soundwire/cadence_master.c
>> index 5d9729b4d634..89c55e4bb72c 100644
>> --- a/drivers/soundwire/cadence_master.c
>> +++ b/drivers/soundwire/cadence_master.c
>> @@ -48,6 +48,8 @@
>>   #define CDNS_MCP_SSPSTAT            0xC
>>   #define CDNS_MCP_FRAME_SHAPE            0x10
>>   #define CDNS_MCP_FRAME_SHAPE_INIT        0x14
>> +#define CDNS_MCP_FRAME_SHAPE_COL_MASK        GENMASK(2, 0)
>> +#define CDNS_MCP_FRAME_SHAPE_ROW_OFFSET        3
>>   #define CDNS_MCP_CONFIG_UPDATE            0x18
>>   #define CDNS_MCP_CONFIG_UPDATE_BIT        BIT(0)
>> @@ -175,7 +177,6 @@
>>   /* Driver defaults */
>>   #define CDNS_DEFAULT_CLK_DIVIDER        0
>> -#define CDNS_DEFAULT_FRAME_SHAPE        0x30
>>   #define CDNS_DEFAULT_SSP_INTERVAL        0x18
>>   #define CDNS_TX_TIMEOUT                2000
>> @@ -901,6 +902,20 @@ int sdw_cdns_pdi_init(struct sdw_cdns *cdns,
>>   }
>>   EXPORT_SYMBOL(sdw_cdns_pdi_init);
>> +static u32 cdns_set_initial_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) & CDNS_MCP_FRAME_SHAPE_COL_MASK;
>> +
>> +    val = (r << CDNS_MCP_FRAME_SHAPE_ROW_OFFSET) | c;
>> +
>> +    return val;
>> +}
>> +
> 
> Guess this have been said already, but this function could be simplified 
> - unless you really want to keep explicit variable declaration. Both "c" 
> and "r" declarations could be merged into single line while "val" is not 
> needed at all.
> 
> One more thing - is AND bitwise op really needed for cols explicitly? We 
> know all col values upfront - these are static and declared in global 
> table nearby. Static declaration takes care of "initial range-check". Is 
> another one necessary?
> 
> Moreover, this is a _get_ and certainly not a _set_ type of function. 
> I'd even consider renaming it to: "cdns_get_frame_shape" as this is 
> neither a _set_ nor an explicit initial frame shape setter.
> 
> It might be even helpful to split two usages:
> 
> #define sdw_frame_shape(col_idx, row_idx) \
>      ((row_idx << CDNS_MCP_FRAME_SHAPE_ROW_OFFSET) | col_idx)
> 
> u32 cdns_get_frame_shape(u16 rows, u16 cols)
> {
>      u16 c, r;
> 
>      r = sdw_find_row_index(rows);
>      c = sdw_find_col_index(cols);
> 
>      return sdw_frame_shape(c, r);
> }
> 
> The above may even be simplified into one-liner.

This is a function used once on startup, there is no real need to 
simplify further. The separate variables help add debug traces as needed 
and keep the code readable while showing how the values are encoded into 
a register.