linux-kernel - Re: [PATCH] DMA: TXx9 Soc DMA Controller driver (v2)

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Date:	Sat, 18 Apr 2009 13:05:15 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Atsushi Nemoto <anemo@....ocn.ne.jp>
Cc:	linux-mips@...ux-mips.org, ralf@...ux-mips.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] DMA: TXx9 Soc DMA Controller driver (v2)

On Mon, Apr 6, 2009 at 8:54 AM, Atsushi Nemoto <anemo@....ocn.ne.jp> wrote:
> This patch adds support for the integrated DMAC of the TXx9 family.
>
> Signed-off-by: Atsushi Nemoto <anemo@....ocn.ne.jp>
> ---

Not quite "ackable" yet...

> +#ifdef CONFIG_MACH_TX49XX
> +#define TXX9_DMA_MAY_HAVE_64BIT_REGS
> +#define TXX9_DMA_HAVE_CCR_LE
> +#define TXX9_DMA_HAVE_SMPCHN
> +#define TXX9_DMA_HAVE_IRQ_PER_CHAN
> +#endif
> +
> +#ifdef TXX9_DMA_HAVE_SMPCHN
> +#define TXX9_DMA_USE_SIMPLE_CHAIN
> +#endif
> +

There seems to be a lot of ifdef magic in the code based on these
defines.  Can we move this magic and some of the pure definitions to
drivers/dma/txx9dmac.h?  (See the "#ifdefs are ugly" section of
Documentation/SubmittingPatches)

> +static struct dma_async_tx_descriptor *
> +txx9dmac_prep_dma_memcpy(struct dma_chan *chan, dma_addr_t dest, dma_addr_t src,
> +               size_t len, unsigned long flags)
[..]
> +               if (!first) {
> +                       first = desc;
> +               } else {
> +                       desc_write_CHAR(dc, prev, desc->txd.phys);
> +                       dma_sync_single_for_device(chan2parent(&dc->chan),
> +                                       prev->txd.phys, ddev->descsize,
> +                                       DMA_TO_DEVICE);
> +                       list_add_tail(&desc->desc_node,
> +                                       &first->txd.tx_list);
> +               }

Is there a reason to keep f'irst' off of the tx_list?  It seems like
you could simplify this logic and get rid of the scary looking
list_splice followed by list_add in txx9dmac_desc_put.  It also seems
odd that the descriptors on tx_list are not reachable from the
dc->queue list after a submit... but maybe I am missing a subtle
detail?

Regards,
Dan
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