linux-kernel - Re: [PATCH 2/6] dmaengine: sun6i: Add a quirk for additional mbus clock

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Date:   Fri, 22 Mar 2019 14:03:25 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Vinod Koul <vkoul@...nel.org>
Cc:     Jernej Škrabec <jernej.skrabec@...l.net>,
        wens@...e.org, robh+dt@...nel.org, mark.rutland@....com,
        dan.j.williams@...el.com, dmaengine@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-sunxi@...glegroups.com
Subject: Re: [PATCH 2/6] dmaengine: sun6i: Add a quirk for additional mbus
 clock

On Fri, Mar 22, 2019 at 06:29:40PM +0530, Vinod Koul wrote:
> On 16-03-19, 12:23, Jernej Škrabec wrote:
> > Hi!
> >
> > Dne sobota, 16. marec 2019 ob 12:07:53 CET je Vinod Koul napisal(a):
> > > On 07-03-19, 17:58, Jernej Skrabec wrote:
> > > > H6 DMA controller needs additional mbus clock to be enabled.
> > > >
> > > > Add a quirk for it and handle it accordingly.
> > > >
> > > > Signed-off-by: Jernej Skrabec <jernej.skrabec@...l.net>
> > > > ---
> > > >
> > > >  drivers/dma/sun6i-dma.c | 23 ++++++++++++++++++++++-
> > > >  1 file changed, 22 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/dma/sun6i-dma.c b/drivers/dma/sun6i-dma.c
> > > > index 0cd13f17fc11..761555080325 100644
> > > > --- a/drivers/dma/sun6i-dma.c
> > > > +++ b/drivers/dma/sun6i-dma.c
> > > > @@ -129,6 +129,7 @@ struct sun6i_dma_config {
> > > >
> > > >  	u32 dst_burst_lengths;
> > > >  	u32 src_addr_widths;
> > > >  	u32 dst_addr_widths;
> > > >
> > > > +	bool mbus_clk;
> > > >
> > > >  };
> > > >
> > > >  /*
> > > >
> > > > @@ -182,6 +183,7 @@ struct sun6i_dma_dev {
> > > >
> > > >  	struct dma_device	slave;
> > > >  	void __iomem		*base;
> > > >  	struct clk		*clk;
> > > >
> > > > +	struct clk		*clk_mbus;
> > >
> > > So rather than have mbus_clk and then a ptr, why not use the ptr and use
> > > NULL value to check for..?
> > >
> >
> > I'm not sure what you mean here. clk_mbus will hold a reference to a clock
> > retrieved by devm_clk_get() so it has to be "struct clk *".
> >
> > What I'm missing here?
>
> IIRC there were two variable one clk ptr and one an integer to mark
> presence, you may be able to skip variable and use ptr..

If we're doing that, then we would effectively make it optional. That
DMA engine cannot operate without it.

Maxime

--
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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