On Thu, Jan 22, 2015 at 5:45 PM, Wolfram Sang <wsa@xxxxxxxxxxxxx> wrote:
>> @@ -320,9 +322,23 @@ static int ocores_i2c_of_probe(struct platform_device *pdev,
>> }
>>
>> if (of_property_read_u32(np, "clock-frequency", &val)) {
>> - dev_err(&pdev->dev,
>> - "Missing required parameter 'clock-frequency'\n");
>> - return -ENODEV;
>> + struct clk *clk = devm_clk_get(&pdev->dev, NULL);
>> +
>> + if (!IS_ERR(clk)) {
>> + int ret = clk_prepare_enable(clk);
>> +
>> + if (ret) {
>> + dev_err(&pdev->dev,
>> + "clk_prepare_enable failed: %d\n", ret);
>> + return ret;
>> + }
>> + i2c->clk = clk;
>> + val = clk_get_rate(clk);
>> + } else {
>> + dev_err(&pdev->dev,
>> + "Missing required parameter 'clock-frequency'\n");
>> + return -ENODEV;
>> + }
>
> Either NAK or I don't understand the logic here :) If a dts does NOT
> have the bus-speed set by 'clock-frequency', then we take the value of
> the clock assigned to this platform_device?
>
> The usual thing to do when 'clock-frequency' is not set is to default to
> 100kHz.
The clock here is not the i2c bus clock, but the clock input of the
controller. The function ocores_init initializes the prescaler register of
the controller so that the bus clock equals 100kHz (internal clock
runs at 500kHz):
static void ocores_init(struct ocores_i2c *i2c)
{
int prescale;
...
prescale = (i2c->clock_khz / (5*100)) - 1;
oc_setreg(i2c, OCI2C_PRELOW, prescale & 0xff);
oc_setreg(i2c, OCI2C_PREHIGH, prescale >> 8);
...
Then yes, when there's no 'clock-frequency' we take the value of the
clock assigned to this platform_device, which in turn comes from the
'clk' property.
--
Thanks.
-- Max
--
To unsubscribe from this list: send the line "unsubscribe linux-i2c" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
