linux-kernel - Re: [PATCH] dma : EG20T PCH: Fix miss-setting DMA descriptor

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Message-ID: <AANLkTi=BOYUwEAxWBhYVhco-Eo2n1isbb_kbJkao11XP@mail.gmail.com>
Date:	Fri, 3 Dec 2010 17:33:45 -0800
From:	Dan Williams <dan.j.williams@...el.com>
To:	Tomoya MORINAGA <tomoya-linux@....okisemi.com>
Cc:	linux-kernel@...r.kernel.org, kok.howg.ewe@...el.com,
	"Wang Qi\"" <qi.wang@...el.com>,
	"Wang Yong Y\"" <yong.y.wang@...el.com>,
	"Intel OTC\"" <joel.clark@...el.com>, margie.foster@...el.com,
	"Andrew\"" <andrew.chih.howe.khor@...el.com>
Subject: Re: [PATCH] dma : EG20T PCH: Fix miss-setting DMA descriptor

2010/12/1 Tomoya MORINAGA <tomoya-linux@....okisemi.com>:
> From: Tomoya MORINAGA <tomoya-linux@....okisemi.com>
>
>
>
> Currently, in case of using scatter/gather mode, head of data is not sent to
>
> destination. The cause is second descriptor address is set to NEXT.
>
> The NEXT must have head of descriptor address.
>
> This patch sets head of descriptor address to the NEXT.
>
>
>
> Signed-off-by: Tomoya MORINAGA <tomoya-linux@....okisemi.com>
> ---
>  drivers/dma/pch_dma.c |   15 ++++++++-------
>  1 files changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/dma/pch_dma.c b/drivers/dma/pch_dma.c
> index 92b6790..a3d54c0 100644
> --- a/drivers/dma/pch_dma.c
> +++ b/drivers/dma/pch_dma.c
[..]
> @@ -273,10 +268,16 @@ static void pdc_dostart(struct pch_dma_chan *pd_chan, struct pch_dma_desc* desc)
>        dev_dbg(chan2dev(&pd_chan->chan), "chan %d -> next: %x\n",
>                pd_chan->chan.chan_id, desc->regs.next);
>
> -       if (list_empty(&desc->tx_list))
> +       if (list_empty(&desc->tx_list)) {
> +               channel_writel(pd_chan, DEV_ADDR, desc->regs.dev_addr);
> +               channel_writel(pd_chan, MEM_ADDR, desc->regs.mem_addr);
> +               channel_writel(pd_chan, SIZE, desc->regs.size);
> +               channel_writel(pd_chan, NEXT, desc->regs.next);
>                pdc_set_mode(&pd_chan->chan, DMA_CTL0_ONESHOT);
> -       else
> +       } else {
> +               channel_writel(pd_chan, NEXT, virt_to_phys(&desc->regs));

There is a reason for the following comment for virt_to_phys():

/*      This function does not give bus mappings for DMA transfers. In
 *      almost all conceivable cases a device driver should not be using
 *      this function
 */

...in this case this wants to be:

     channel_write(pd_chan, NEXT, desc->txd.phys);

I'll let Yong comment on the correctness of the rest.

--
Dan
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