From: zonque@gmail•com (Daniel Mack)
To: linux-arm-kernel@lists•infradead.org
Subject: [v3 1/2] dma: mmp_pdma: add support for residue reporting
Date: Fri, 16 Aug 2013 17:40:06 +0200 [thread overview]
Message-ID: <520E47D6.8020000@gmail.com> (raw)
In-Reply-To: <520DDB81.20607@marvell.com>
On 16.08.2013 09:57, Xiang Wang wrote:
> On 08/15/2013 12:19 AM, Daniel Mack wrote:
>> In order to report the channel's residue, we have to memorize the first
>> dma buffer position when the channel is configured.
>>
>> Signed-off-by: Daniel Mack <zonque@gmail•com>
>> ---
>> drivers/dma/mmp_pdma.c | 45 +++++++++++++++++++++++++++++++++++++++++++--
>> 1 file changed, 43 insertions(+), 2 deletions(-)
>>
>
>> +static unsigned int mmp_pdma_residue(struct mmp_pdma_chan *chan)
>> +{
>> + struct mmp_pdma_desc_sw *sw;
>> + u32 curr, done = 0;
>> +
>> + if (chan->dir == DMA_DEV_TO_MEM)
>> + curr = readl(chan->phy->base + DTADR(chan->phy->idx));
> One concern for this patch:
> If we call dmaengine_tx_status() after dma_do_tasklet at mmp_pdma.c,
> chan->phy will most likely to be NULL.
> dma_do_tasklet() -> start_pending_queue() -> mmp_pdma_free_phy()
Yes, I noticed this, too. I'm not really sure what the reason is to call
start_pending_queue() _before_ the callbacks are done. A quick test
shows that it works as well the other way around.
> For why do we call dmaengine_tx_status() after a DMA interrupt:
> briefly, if we use DMA to handle device trailing bytes, it'll report a
> DMA interrupt. We need to get to know how many bytes have been received
> in the IRQ handler.
> We've discussed about this in the link below:
> http://thread.gmane.org/gmane.linux.kernel/1500713
Thanks for the link, I wasn't aware of that discussion. And I actually
second what Andy said: As long as the residue calculation algorithm can
cope with the chan->phy==NULL condition and return 0 in that case, it's
actually doing the right thing, because a completed transaction has a
residue of 0 bytes.
I'll send out another series later, that also aims to fix the tasklet
behaviour. I'd appreciate another round of reviews :)
Daniel
prev parent reply other threads:[~2013-08-16 15:40 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-14 16:19 [v3 1/2] dma: mmp_pdma: add support for residue reporting Daniel Mack
2013-08-14 16:23 ` Russell King - ARM Linux
2013-08-15 1:57 ` Chao Xie
2013-08-15 3:44 ` Daniel Mack
2013-08-15 8:08 ` Chao Xie
2013-08-15 18:12 ` Daniel Mack
2013-08-16 2:21 ` Chao Xie
2013-08-16 7:57 ` Xiang Wang
2013-08-16 15:40 ` Daniel Mack [this message]
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