Re: [PATCH 1/4] dmaengine: qcom: bam_dma: make bam clk optional

[Srinivas Kandagatla]

On 19/01/18 05:52, Vinod Koul wrote:
> On Tue, Jan 16, 2018 at 07:02:33PM +0000, srinivas.kandagatla@xxxxxxxxxx wrote:
> > From: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
> >
> > When BAM is remotely controlled it does not sound correct to control
> > its clk on Linux side. Make it optional, so that its not madatory
>
> s/madatory/mandatory
Yep,
> > for remote controlled BAM instances.
> >
> > Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
> > ---
> >   drivers/dma/qcom/bam_dma.c | 15 ++++++++-------
> >   1 file changed, 8 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/dma/qcom/bam_dma.c b/drivers/dma/qcom/bam_dma.c
> > index 03c4eb3fd314..78e488e8f96d 100644
> > --- a/drivers/dma/qcom/bam_dma.c
> > +++ b/drivers/dma/qcom/bam_dma.c
> > @@ -1180,13 +1180,14 @@ static int bam_dma_probe(struct platform_device *pdev)
> >   						"qcom,controlled-remotely");
> >   
> >   	bdev->bamclk = devm_clk_get(bdev->dev, "bam_clk");
>
> but you still do clk_get unconditionally?

Only reason to do this way is to not break existing users in the mainline.

remotely controlled BAM is already supported in upstream driver, there 
are users of this who pass clk from device tree, If I make this 
conditional then subsequent reads to the BAM registers for those 
instances might crash the system.

This sounds wrong to control clk from linux for the dma controller which 
is remotely controlled. These users should be transitioned to new 
bindings once the new bindings endup in the mainline.

> > -	if (IS_ERR(bdev->bamclk))
> > -		return PTR_ERR(bdev->bamclk);
> > -
> > -	ret = clk_prepare_enable(bdev->bamclk);
> > -	if (ret) {
> > -		dev_err(bdev->dev, "failed to prepare/enable clock\n");
> > -		return ret;
> > +	if (IS_ERR(bdev->bamclk)) {
> > +		bdev->bamclk = NULL;
> > +	} else {
> > +		ret = clk_prepare_enable(bdev->bamclk);
> > +		if (ret) {
> > +			dev_err(bdev->dev, "failed to prepare/enable clock\n");
> > +			return ret;
> > +		}
>
> wouldn't it be better to set that an instance is remote controlled and thus
> not at all visible to Linux?

We already have a flag "controlled_remotely" for that in the driver.

thanks,
srini
> >   	}
> >   
> >   	ret = bam_init(bdev);
> > --
> > 2.15.1
> >
> > --
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