Re: [PATCH 1/3] RFC: AHCI: libahci is missing DMA

[Oliver Schinagl]

Hey Tejun Heo,

On 04-12-13 13:32, Tejun Heo wrote:
> On Wed, Dec 04, 2013 at 01:10:53PM +0100, oliver@xxxxxxxxxxx wrote:
> > From: Oliver Schinagl <oliver@xxxxxxxxxxx>
> >
> > The Allwinner sunxi platforms have patched in the following to enable
> > DMA. This patch enables DMA controllers for the SUNXI Architecture.
> >
> > Signed-off-by: Olliver Schinagl <oliver@xxxxxxxxxxx>
> > ---
> >   drivers/ata/ahci.h    | 6 ++++++
> >   drivers/ata/libahci.c | 8 ++++++++
> >   2 files changed, 14 insertions(+)
> >
> > diff --git a/drivers/ata/ahci.h b/drivers/ata/ahci.h
> > index 2289efdf..2bf2423 100644
> > --- a/drivers/ata/ahci.h
> > +++ b/drivers/ata/ahci.h
> > @@ -138,6 +138,7 @@ enum {
> >   	PORT_SCR_NTF		= 0x3c, /* SATA phy register: SNotification */
> >   	PORT_FBS		= 0x40, /* FIS-based Switching */
> >   	PORT_DEVSLP		= 0x44, /* device sleep */
> > +	PORT_DMA		= 0x70, /* direct memory access */
> >   
> >   	/* PORT_IRQ_{STAT,MASK} bits */
> >   	PORT_IRQ_COLD_PRES	= (1 << 31), /* cold presence detect */
> > @@ -209,6 +210,11 @@ enum {
> >   	PORT_DEVSLP_DSP		= (1 << 1),       /* DevSlp present */
> >   	PORT_DEVSLP_ADSE	= (1 << 0),       /* Aggressive DevSlp enable */
> >   
> > +	/* PORT_DMA bits */
> > +	PORT_DMA_SETUP_OFFSET	= 8, /* dma setup offset */
> > +	PORT_DMA_SETUP_MASK	= (0xff << PORT_DMA_SETUP_OFFSET),/* dma mask */
> > +	PORT_DMA_SETUP_INIT	= (0x44 << 0),
> Ummm... this doesn't belong to ahci proper, right?
I have no idea why Allwinner added that and what it really does. We have 
no documentation, only code drops.

I had high hopes someone around here knows what it could mean and where 
it does belong.
> > +
> >   	/* hpriv->flags bits */
> >   
> >   #define AHCI_HFLAGS(flags)		.private_data	= (void *)(flags)
> > diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c
> > index c482f8c..d697a74 100644
> > --- a/drivers/ata/libahci.c
> > +++ b/drivers/ata/libahci.c
> > @@ -570,6 +570,14 @@ void ahci_start_engine(struct ata_port *ap)
> >   	void __iomem *port_mmio = ahci_port_base(ap);
> >   	u32 tmp;
> >   
> > +#ifdef CONFIG_ARCH_SUNXI
> > +	/* Setup DMA before DMA start */
> > +	tmp = readl(port_mmio + PORT_DMA);
> > +	tmp &= ~PORT_DMA_SETUP_MASK;
> > +	tmp |= PORT_DMA_SETUP_INIT << PORT_DMA_SETUP_OFFSET;
> > +	writel(tmp, port_mmio + PORT_DMA);
> > +#endif
> If this is something platform device specific, wouldn't overriding
> ->port_start() which wraps around ahci_port_start() make more sense?
Again, I don't know, this is where Allwinner had put it. We don't even 
know who's IP they use. I'm happy to start experimenting moving this 
around a bit and will take your clue to figure out what you mean and if 
it could work.

Oliver
> Thanks.

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