Messages in this thread | | | Date | Mon, 19 Sep 2022 13:18:59 +0000 | From | Sakari Ailus <> | Subject | Re: [PATCH v2 1/3] media: mt9m111: add V4L2_CID_LINK_FREQ support |
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Hi Marco,
On Mon, Sep 19, 2022 at 03:08:29PM +0200, Marco Felsch wrote: > Hi Sakari, > > On 22-09-19, Sakari Ailus wrote: > > Hi Marco, > > > > On Fri, Sep 16, 2022 at 03:57:11PM +0200, Marco Felsch wrote: > > > Add support to report the link frequency. > > > > > > Signed-off-by: Marco Felsch <m.felsch@pengutronix.de> > > > --- > > > The v1 of this small series can be found here: > > > https://lore.kernel.org/all/20220818144712.997477-1-m.felsch@pengutronix.de/ > > > > > > Thanks a lot to Jacopo for the review feedback on my v1. > > > > > > Changelog: > > > > > > v2: > > > - use V4L2_CID_LINK_FREQ instead of V4L2_CID_PIXEL_RATE > > > --- > > > drivers/media/i2c/mt9m111.c | 21 ++++++++++++++++++++- > > > 1 file changed, 20 insertions(+), 1 deletion(-) > > > > > > diff --git a/drivers/media/i2c/mt9m111.c b/drivers/media/i2c/mt9m111.c > > > index afc86efa9e3e..52be1c310455 100644 > > > --- a/drivers/media/i2c/mt9m111.c > > > +++ b/drivers/media/i2c/mt9m111.c > > > @@ -1249,6 +1249,8 @@ static int mt9m111_probe(struct i2c_client *client) > > > { > > > struct mt9m111 *mt9m111; > > > struct i2c_adapter *adapter = client->adapter; > > > + static s64 extclk_rate; > > > + struct v4l2_ctrl *ctrl; > > > int ret; > > > > > > if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_WORD_DATA)) { > > > @@ -1271,6 +1273,13 @@ static int mt9m111_probe(struct i2c_client *client) > > > if (IS_ERR(mt9m111->clk)) > > > return PTR_ERR(mt9m111->clk); > > > > > > + ret = clk_prepare_enable(mt9m111->clk); > > > + if (ret < 0) > > > + return ret; > > > + > > > + extclk_rate = clk_get_rate(mt9m111->clk); > > > + clk_disable_unprepare(mt9m111->clk); > > > > I don't think you'll need to enable a clock to just get its frequency. > > The official API states that you need to turn on the clk before > requesting it and it makes sense. Also there is a new helper > devm_clk_get_enabled() which addresses simple clk usage since most of > drivers don't enable it before requesting the rate.
I guess the rate could change in the meantime, unless exclusive access is requested. The clock framework currently doesn't offer a way to set the assigned rate and prevent changing it. But above, couldn't the clock frequency be changed again once the clock has been disabled?
-- Sakari Ailus
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