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

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Date:	Wed, 04 Dec 2013 14:09:14 +0100
From:	Oliver Schinagl <oliver@...inagl.nl>
To:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
CC:	tj@...nel.org, grant.likely@...aro.org,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, dev@...ux-sunxi.org,
	maxime.ripard@...e-electrons.com, ijc@...lion.org.uk,
	hdegoede@...hat.com, oliver+list@...inagl.nl
Subject: Re: [PATCH 1/3] RFC: AHCI: libahci is missing DMA


On 04-12-13 13:47, Sergei Shtylyov wrote:
> Hello.
>
> On 04-12-2013 16:10, oliver@...inagl.nl wrote:
>
>> From: Oliver Schinagl <oliver@...inagl.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@...inagl.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
> [...]
>> @@ -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),
>
>    Why not shift it right by PORT_DMA_SETUP_OFFSET if you do it in the 
> next file anyway?
Verbosity and clarity I suppose, try to reduce the number of magic 
values. I don't know what the preferred way is as we know so little 
about the IP.
>
> [...]
>> 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
>> +
>
>    I don't think #ifdef is appropriate here.
It's not, but I was hoping Smarter devs then me would point me the right 
way ;)

Oliver
>
> WBR, Sergei
>

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