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Date: Tue, 22 Jan 2013 13:41:58 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Vinod Koul <vinod.koul@...el.com>, linux-kernel@...r.kernel.org,
spear-devel <spear-devel@...t.st.com>
Subject: Re: [PATCH 2/2] dw_dmac: return proper residue value
On Mon, Jan 21, 2013 at 2:30 PM, Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
> Currently the driver returns full length of the active descriptor which is
> wrong. We have to go throught the active descriptor and sum up the length of
> unsent children in the chain along with the actual data in the DMA channel
> registers.
>
> The cyclic case is not handled by this patch due to len field in the descriptor
> structure is left untouched by the original code.
>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
> drivers/dma/dw_dmac.c | 93 ++++++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 92 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/dma/dw_dmac.c b/drivers/dma/dw_dmac.c
> index d1b9ba2..4325c68 100644
> --- a/drivers/dma/dw_dmac.c
> +++ b/drivers/dma/dw_dmac.c
> @@ -941,6 +941,97 @@ err_desc_get:
> return NULL;
> }
>
> +/* --------------------- Calculate residue ---------------------------- */
> +
> +static inline size_t dwc_get_rest(struct dw_dma_chan *dwc, struct dw_desc *desc)
> +{
> + enum dma_transfer_direction direction = dwc->direction;
> +
> + if (direction == DMA_MEM_TO_DEV || direction == DMA_MEM_TO_MEM)
> + return desc->len - (channel_readl(dwc, SAR) - desc->lli.sar);
> + else if (direction == DMA_DEV_TO_MEM)
> + return desc->len - (channel_readl(dwc, DAR) - desc->lli.dar);
> +
> + return 0;
> +}
I agree with Vinod on this routine.
> +static inline size_t dwc_get_residue_in_llp(struct dw_dma_chan *dwc,
> + struct list_head *active,
> + struct list_head *head)
> +{
> + size_t residue = dwc_get_rest(dwc, to_dw_desc(active));
> +
> + do {
> + active = active->next;
> + if (active == head)
> + break;
> + residue += to_dw_desc(active)->len;
> + } while (true);
> +
> + return residue;
> +}
> +
> +static size_t dwc_calc_residue_llp_hw(struct dw_dma_chan *dwc)
> +{
> + struct dw_desc *desc = dwc_first_active(dwc);
> + struct list_head *head = &desc->tx_list, *active;
> + dma_addr_t llp = channel_readl(dwc, LLP);
> +
> + /* The transfer didn't start yet */
> + if (unlikely(desc->txd.phys == llp))
> + return desc->len;
> +
> + /* First descriptor is active */
> + if (desc->lli.llp == llp)
> + return dwc_get_rest(dwc, desc);
> +
> + /* Somewhere in the middle */
> + list_for_each(active, head)
> + if (to_dw_desc(active)->lli.llp == llp)
> + return dwc_get_residue_in_llp(dwc, active, head);
> +
> + return 0;
> +}
> +
> +static size_t dwc_calc_residue_llp_sw(struct dw_dma_chan *dwc)
> +{
> + struct dw_desc *desc = dwc_first_active(dwc);
> + struct list_head *head = dwc->tx_list, *active;
> +
> + active = dwc->tx_node_active;
> +
> + /* First node is active */
> + if (active == head->next)
> + return dwc_get_rest(dwc, desc);
> +
> + /* Last node is active */
> + if (active == head)
> + return dwc_get_rest(dwc, to_dw_desc(active->prev));
> +
> + /* Somewhere in the middle */
> + return dwc_get_residue_in_llp(dwc, active, head);
> +}
> +
> +static size_t dwc_get_residue(struct dw_dma_chan *dwc)
return u32, that's the type of residue field.
> +{
> + unsigned long flags;
> + size_t residue = 0;
ditto.
> +
> + spin_lock_irqsave(&dwc->lock, flags);
> + if (list_empty(&dwc->active_list)) {
can this every happen?
> + spin_unlock_irqrestore(&dwc->lock, flags);
> + return 0;
> + }
> +
> + if (test_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags))
> + residue = dwc_calc_residue_llp_sw(dwc);
> + else if (!test_bit(DW_DMA_IS_CYCLIC, &dwc->flags))
> + residue = dwc_calc_residue_llp_hw(dwc);
Hmm. you return zero for cyclic transfers, shouldn't that be the total
length instead?
Over that, cyclic case can be handled before taking any locks.
> +
> + spin_unlock_irqrestore(&dwc->lock, flags);
> + return residue;
> +}
> +
> /*
> * Fix sconfig's burst size according to dw_dmac. We need to convert them as:
> * 1 -> 0, 4 -> 1, 8 -> 2, 16 -> 3.
> @@ -1062,7 +1153,7 @@ dwc_tx_status(struct dma_chan *chan,
> }
>
> if (ret != DMA_SUCCESS)
> - dma_set_residue(txstate, dwc_first_active(dwc)->len);
> + dma_set_residue(txstate, dwc_get_residue(dwc));
Hmm.. After thinking a bit more on this, i am not sure if what u have done is
the best way of doing it :(
Just before above line got executed, we called dwc_scan_descriptors(), which
also scans through the llis to see where we are.. What about updating
first->residue
there, so that we don't traverse it twice?
>
> if (dwc->paused)
> return DMA_PAUSED;
> --
> 1.7.10.4
>
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