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Date: Thu, 24 Jan 2013 10:01:23 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Viresh Kumar <viresh.kumar@...aro.org>
Cc: Vinod Koul <vinod.koul@...el.com>, linux-kernel@...r.kernel.org,
spear-devel <spear-devel@...t.st.com>
Subject: Re: [PATCH v2 4/4] dw_dmac: return proper residue value
On Thu, 2013-01-24 at 10:37 +0530, Viresh Kumar wrote:
> On Wed, Jan 23, 2013 at 9:07 PM, Andy Shevchenko
> <andriy.shevchenko@...ux.intel.com> wrote:
> > diff --git a/drivers/dma/dw_dmac.c b/drivers/dma/dw_dmac.c
>
> > static void dwc_scan_descriptors(struct dw_dma *dw, struct dw_dma_chan *dwc)
> > {
> > dma_addr_t llp;
> > @@ -410,6 +441,8 @@ static void dwc_scan_descriptors(struct dw_dma *dw, struct dw_dma_chan *dwc)
> > */
> > desc = dwc_first_active(dwc);
> >
> > + dwc_update_residue(dwc, desc);
> > +
> > if (dwc->tx_node_active != &desc->tx_list) {
> > child = to_dw_desc(dwc->tx_node_active);
>
> Is there a point updating residue here? I don't have a very good knowledge of
> nollp transfers but this is what i know...
>
> The above "if" will pass if we are still doing transfers and fail if
> all transfers are done.
> After the end of each LLI we receive an interrupt, where we queue next
> LLI. Better
> would be to initialize dwc->residue at dwc_dostart() with total
> length, start decrementing
> it with desc->len for every lli interrupt we get
It's mostly okay, but we have to handle few cases:
- we have only first (master) descriptor
- we have a chain of the descriptors: master + children
- we have finished last transfer
>From my point of view we can't fully get rid of dwc_update_residue(),
but modify it a bit (drop away for loop).
> and if call for
> getting residue comes in
> middle of transfer, simple return residue - dwc_get_sent(desc) without
> updating residue
> field...
Where? In the tx_status to call something which returns dwc->residue -
dwc_get_sent() ?
>
> > @@ -436,6 +469,9 @@ static void dwc_scan_descriptors(struct dw_dma *dw, struct dw_dma_chan *dwc)
> >
> > if (test_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags)) {
> > dev_vdbg(chan2dev(&dwc->chan), "%s: soft LLP mode\n", __func__);
> > +
> > + dwc_update_residue(dwc, dwc_first_active(dwc));
> > +
>
> same is applicable here too and so you can get rid of
> dwc_update_residue() routine.
Same thoughts as above are applicable to this.
> > spin_unlock_irqrestore(&dwc->lock, flags);
> > return;
> > }
> > @@ -444,6 +480,9 @@ static void dwc_scan_descriptors(struct dw_dma *dw, struct dw_dma_chan *dwc)
> > (unsigned long long)llp);
> >
> > list_for_each_entry_safe(desc, _desc, &dwc->active_list, desc_node) {
> > + /* initial residue value */
> > + dwc->residue = desc->total_len;
> > +
> > /* check first descriptors addr */
> > if (desc->txd.phys == llp) {
> > spin_unlock_irqrestore(&dwc->lock, flags);
> > @@ -453,16 +492,21 @@ static void dwc_scan_descriptors(struct dw_dma *dw, struct dw_dma_chan *dwc)
> > /* check first descriptors llp */
> > if (desc->lli.llp == llp) {
> > /* This one is currently in progress */
> > + dwc->residue -= dwc_get_sent(dwc);
> > spin_unlock_irqrestore(&dwc->lock, flags);
> > return;
> > }
> >
> > - list_for_each_entry(child, &desc->tx_list, desc_node)
> > + dwc->residue -= desc->len;
> > + list_for_each_entry(child, &desc->tx_list, desc_node) {
> > if (child->lli.llp == llp) {
> > /* Currently in progress */
> > + dwc->residue -= dwc_get_sent(dwc);
> > spin_unlock_irqrestore(&dwc->lock, flags);
> > return;
> > }
> > + dwc->residue -= child->len;
> > + }
> >
> > /*
> > * No descriptors so far seem to be in progress, i.e.
> > @@ -1058,6 +1102,7 @@ dwc_tx_status(struct dma_chan *chan,
> > struct dma_tx_state *txstate)
> > {
> > struct dw_dma_chan *dwc = to_dw_dma_chan(chan);
> > + unsigned long flags;
> > enum dma_status ret;
> >
> > ret = dma_cookie_status(chan, cookie, txstate);
> > @@ -1067,8 +1112,12 @@ dwc_tx_status(struct dma_chan *chan,
> > ret = dma_cookie_status(chan, cookie, txstate);
> > }
> >
> > + spin_lock_irqsave(&dwc->lock, flags);
> > +
>
> why do you need locking here?
What about the case when one CPU is getting an interrupt and runs
scan_descriptors when the other, for example, in the middle of
tx_status? So, I'm afraid the dma_set_residue(txstate, dwc->residue) is
not atomic and we might end up with random numbers here.
> > if (ret != DMA_SUCCESS)
> > - dma_set_residue(txstate, dwc_first_active(dwc)->len);
> > + dma_set_residue(txstate, dwc->residue);
> > +
> > + spin_unlock_irqrestore(&dwc->lock, flags);
> >
> > if (dwc->paused)
> > return DMA_PAUSED;
> > diff --git a/drivers/dma/dw_dmac_regs.h b/drivers/dma/dw_dmac_regs.h
> > index 833b4cf..88dd8eb 100644
> > --- a/drivers/dma/dw_dmac_regs.h
> > +++ b/drivers/dma/dw_dmac_regs.h
> > @@ -203,6 +203,7 @@ struct dw_dma_chan {
> > struct list_head active_list;
> > struct list_head queue;
> > struct list_head free_list;
> > + u32 residue;
> > struct dw_cyclic_desc *cdesc;
> >
> > unsigned int descs_allocated;
--
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy
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