linux-kernel - Re: [alsa-devel] [RFC PATCH 25/40] soundwire: intel: use BIOS information to set clock dividers

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Date:   Mon, 5 Aug 2019 10:40:13 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Sanyog Kale <sanyog.r.kale@...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
Subject: Re: [alsa-devel] [RFC PATCH 25/40] soundwire: intel: use BIOS
 information to set clock dividers



On 8/5/19 5:28 AM, Sanyog Kale wrote:
> On Thu, Jul 25, 2019 at 06:40:17PM -0500, Pierre-Louis Bossart wrote:
>> The BIOS provides an Intel-specific property, let's use it to avoid
>> hard-coded clock dividers.
>>
>> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
>> ---
>>   drivers/soundwire/cadence_master.c | 26 ++++++++++++++++++++++----
>>   drivers/soundwire/intel.c          | 26 ++++++++++++++++++++++++++
>>   include/linux/soundwire/sdw.h      |  2 ++
>>   3 files changed, 50 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/soundwire/cadence_master.c b/drivers/soundwire/cadence_master.c
>> index d84344e29f71..10ebcef2e84e 100644
>> --- a/drivers/soundwire/cadence_master.c
>> +++ b/drivers/soundwire/cadence_master.c
>> @@ -173,8 +173,6 @@
>>   #define CDNS_PDI_CONFIG_PORT			GENMASK(4, 0)
>>   
>>   /* Driver defaults */
>> -
>> -#define CDNS_DEFAULT_CLK_DIVIDER		0
>>   #define CDNS_DEFAULT_SSP_INTERVAL		0x18
>>   #define CDNS_TX_TIMEOUT				2000
>>   
>> @@ -973,7 +971,10 @@ static u32 cdns_set_default_frame_shape(int n_rows, int n_cols)
>>    */
>>   int sdw_cdns_init(struct sdw_cdns *cdns)
>>   {
>> +	struct sdw_bus *bus = &cdns->bus;
>> +	struct sdw_master_prop *prop = &bus->prop;
>>   	u32 val;
>> +	int divider;
>>   	int ret;
>>   
>>   	/* Exit clock stop */
>> @@ -985,9 +986,17 @@ int sdw_cdns_init(struct sdw_cdns *cdns)
>>   	}
>>   
>>   	/* Set clock divider */
>> +	divider	= (prop->mclk_freq / prop->max_clk_freq) - 1;
> 
> Do you expect mclk_freq and max_clk_freq to be same?

Nope. For Icelake the MCLK is 38.4 MHz and is, but the max_clk needs to 
be 9.6 max (can't be higher per the SoundWire spec).

The max_clk_freq may even be lower thank 9.6 MHz due to specific 
topologies where the higher frequencies are problematic if the trace 
lengths are too long.

For CNL/CML the MCLK is 24 MHz but ironically we run the bus at 12 MHz, 
so the divider is smaller.

> 
>>   	val = cdns_readl(cdns, CDNS_MCP_CLK_CTRL0);
>> -	val |= CDNS_DEFAULT_CLK_DIVIDER;
>> +	val |= divider;
>>   	cdns_writel(cdns, CDNS_MCP_CLK_CTRL0, val);
>> +	cdns_writel(cdns, CDNS_MCP_CLK_CTRL1, val);
>> +
>> +	pr_err("plb: mclk %d max_freq %d divider %d register %x\n",
>> +	       prop->mclk_freq,
>> +	       prop->max_clk_freq,
>> +	       divider,
>> +	       val);
> 
> This can be removed.

yes, done already.

> 
>>   
>>   	/* Set the default frame shape */
>>   	val = cdns_set_default_frame_shape(prop->default_row,
>> @@ -1035,6 +1044,7 @@ EXPORT_SYMBOL(sdw_cdns_init);
>>   
>>   int cdns_bus_conf(struct sdw_bus *bus, struct sdw_bus_params *params)
>>   {
>> +	struct sdw_master_prop *prop = &bus->prop;
>>   	struct sdw_cdns *cdns = bus_to_cdns(bus);
>>   	int mcp_clkctrl_off, mcp_clkctrl;
>>   	int divider;
>> @@ -1044,7 +1054,9 @@ int cdns_bus_conf(struct sdw_bus *bus, struct sdw_bus_params *params)
>>   		return -EINVAL;
>>   	}
>>   
>> -	divider	= (params->max_dr_freq / params->curr_dr_freq) - 1;
>> +	divider	= prop->mclk_freq * SDW_DOUBLE_RATE_FACTOR /
> 
> What is the reason for not using max_dr_freq? Its precomputed as
> prop->max_clk_freq * SDW_DOUBLE_RATE_FACTOR;

no, as explained above the divider needs to start from the clock 
provided to the IP, which is different from the max frequency clock the 
bus operates at. the MCLK is a fixed value for all platforms using the 
same SOC/PCH, the max_clk is platform-dependent and its value is 
provided by the firmware (BIOS/DT).