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SubjectRe: [PATCH 1/3] RFC: AHCI: libahci is missing DMA
Hey Tejun Heo,

On 04-12-13 13:32, Tejun Heo wrote:
> On Wed, Dec 04, 2013 at 01:10:53PM +0100, oliver@schinagl.nl wrote:
>> From: Oliver Schinagl <oliver@schinagl.nl>
>>
>> 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@schinagl.nl>
>> ---
>> 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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