Re: [PATCH] drivers: dma: qcom: bam_dma: Manage clocks when controlled_remotely is set

[Thara Gopinath]

Hi Shawn,

On 1/23/21 2:19 AM, Shawn Guo wrote:
> On Fri, Jan 22, 2021 at 10:44:09AM -0500, Thara Gopinath wrote:
> > Hi Shawn,
> >
> > Thanks for the review
> >
> > On 1/22/21 12:10 AM, Shawn Guo wrote:
> > > On Thu, Jan 21, 2021 at 09:52:51PM -0500, Thara Gopinath wrote:
> > > > When bam dma is "controlled remotely", thus far clocks were not controlled
> > > > from the Linux. In this scenario, Linux was disabling runtime pm in bam dma
> > > > driver and not doing any clock management in suspend/resume hooks.
> > > >
> > > > With introduction of crypto engine bam dma, the clock is a rpmh resource
> > > > that can be controlled from both Linux and TZ/remote side.  Now bam dma
> > > > clock is getting enabled during probe even though the bam dma can be
> > > > "controlled remotely". But due to clocks not being handled properly,
> > > > bam_suspend generates a unbalanced clk_unprepare warning during system
> > > > suspend.
> > > >
> > > > To fix the above issue and to enable proper clock-management, this patch
> > > > enables runtim-pm and handles bam dma clocks in suspend/resume hooks if
> > > > the clock node is present irrespective of controlled_remotely property.
> > >
> > > Shouldn't the following probe code need some update?  Now we have both
> > > controlled_remotely and clocks handle for cryptobam node.  For example,
> > > if devm_clk_get() returns -EPROBE_DEFER, we do not want to continue with
> > > bamclk forcing to be NULL, right?
> >
> > We still will have to set bdev->bamclk to NULL in certain scenarios. For eg
> > slimbus bam dma is controlled-remotely and the clocks are handled by the
> > remote s/w. Linux does not handle the clocks at all and  there is no clock
> > specified in the dt node.This is the norm for the devices that are also
> > controlled by remote s/w. Crypto bam dma is a special case where the clock
> > is actually a rpmh resource and hence can be independently handled from both
> > remote side and Linux by voting. In this case, the dma is controlled
> > remotely but clock can be turned off and on in Linux. Hence the need for
> > this patch.
>
> So is it correct to say that clock is mandatory for !controlled-remotely
> BAM, while it's optional for controlled-remotely one.  If yes, maybe we
> can do something like below to make the code a bit easier to read?

Yes. Sure. I will change it to below.

> 	if (controlled-remotely)
> 		bdev->bamclk = devm_clk_get_optional();
> 	else
> 		bdev->bamclk = devm_clk_get();
> 		
> > Yes, the probe code needs updating to handle -EPROBE_DEFER (esp if the clock
> > driver is built in as a module) I am not sure if the clock framework handles
> > -EPROBE_DEFER properly either. So that
> > might need updating too. This is a separate activity and not part of this
> > patch >
>
> As the patch breaks the assumption that for controlled-remotely BAM
> there is no clock to be managed, the probe code becomes buggy right
> away.

mmm... not really. Either ways we don't handle -EPROBE_DEFER from clock 
code. That behavior is not worse because of this patch. I can send a 
separate patch to fix the -EPROBE_DEFER issue.

> Shawn

--
Warm Regards
Thara