Subject: Re: [PATCH v11 3/3] DMA: Freescale: update driver to support 8-channel DMA engine

From: Hongbo Zhang <[email-masked]>
Date: Mon, 11 Nov 2013 17:12:07 +0800

On 11/08/2013 10:45 AM, Dan Williams wrote:
> On Mon, Nov 4, 2013 at 6:31 PM, Hongbo Zhang <[email-masked]> wrote:
>> Hi Vinod Koul and Dan Williams,
>> Ping?
>>
> Not much to review from the dmaengine side, just one question below.
> It would be helpful if you can send these to the new dmaengine
> patchwork at [email-masked] with the Acks you have already
> collected.
>

Sorry didn't notice this new mailing list.
I will resend these patches to it again.

>>
>> On 10/17/2013 01:56 PM, Hongbo Zhang wrote:
>>> Hi Vinod,
>>> I have gotten ACK from Mark for both the 1/3 and 2/3 patches.
>>> Thanks.
>>>
>>>
>>> On 09/26/2013 05:33 PM, [email-masked] wrote:
>>>> From: Hongbo Zhang <[email-masked]>
>>>>
>>>> This patch adds support to 8-channel DMA engine, thus the driver works
>>>> for both
>>>> the new 8-channel and the legacy 4-channel DMA engines.
>>>>
>>>> Signed-off-by: Hongbo Zhang <[email-masked]>
>>>> ---
>>>>    drivers/dma/Kconfig  |    9 +++++----
>>>>    drivers/dma/fsldma.c |    9 ++++++---
>>>>    drivers/dma/fsldma.h |    2 +-
>>>>    3 files changed, 12 insertions(+), 8 deletions(-)
>>>>
>>>> diff --git a/drivers/dma/Kconfig b/drivers/dma/Kconfig
>>>> index 6825957..3979c65 100644
>>>> --- a/drivers/dma/Kconfig
>>>> +++ b/drivers/dma/Kconfig
>>>> @@ -89,14 +89,15 @@ config AT_HDMAC
>>>>          Support the Atmel AHB DMA controller.
>>>>      config FSL_DMA
>>>> -    tristate "Freescale Elo and Elo Plus DMA support"
>>>> +    tristate "Freescale Elo series DMA support"
>>>>        depends on FSL_SOC
>>>>        select DMA_ENGINE
>>>>        select ASYNC_TX_ENABLE_CHANNEL_SWITCH
>>>>        ---help---
>>>> -      Enable support for the Freescale Elo and Elo Plus DMA controllers.
>>>> -      The Elo is the DMA controller on some 82xx and 83xx parts, and the
>>>> -      Elo Plus is the DMA controller on 85xx and 86xx parts.
>>>> +      Enable support for the Freescale Elo series DMA controllers.
>>>> +      The Elo is the DMA controller on some mpc82xx and mpc83xx parts,
>>>> the
>>>> +      EloPlus is on mpc85xx and mpc86xx and Pxxx parts, and the Elo3 is
>>>> on
>>>> +      some Txxx and Bxxx parts.
>>>>      config MPC512X_DMA
>>>>        tristate "Freescale MPC512x built-in DMA engine support"
>>>> diff --git a/drivers/dma/fsldma.c b/drivers/dma/fsldma.c
>>>> index 49e8fbd..16a9a48 100644
>>>> --- a/drivers/dma/fsldma.c
>>>> +++ b/drivers/dma/fsldma.c
>>>> @@ -1261,7 +1261,9 @@ static int fsl_dma_chan_probe(struct fsldma_device
>>>> *fdev,
>>>>        WARN_ON(fdev->feature != chan->feature);
>>>>          chan->dev = fdev->dev;
>>>> -    chan->id = ((res.start - 0x100) & 0xfff) >> 7;
>>>> +    chan->id = (res.start & 0xfff) < 0x300 ?
>>>> +           ((res.start - 0x100) & 0xfff) >> 7 :
>>>> +           ((res.start - 0x200) & 0xfff) >> 7;
>>>>        if (chan->id >= FSL_DMA_MAX_CHANS_PER_DEVICE) {
> Isn't it a bit fragile to have this based on the resource address?
> Can't device tree tell you the channel id directly by an index into
> the "dma0: dma@100300" node?

Yes, both this way and putting a "cell-index" into device tree work.
This won't be fragile, because the resource address should always be 
defined correctly, otherwise even if we can tell a channel id by 
"cell-index" but with wrong resource address, nothing will work.
This piece of code only doesn't seem as neat as using "cell-index", but 
we prefer the style that let the device tree describes as true as what 
hardware really has. This doesn't mean "cell-index" isn't acceptable, if 
it is necessary and unavoidable, we can send another patch to add it, 
but currently there is no need and we don't have to do this.

> --
> Dan