Re: [PATCH V4 04/14] DMA: PL330: Add DMA_CYCLIC capability

From: Vinod Koul <vkoul@infradead.org>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: linux-samsung-soc@vger.kernel.org,
	Boojin Kim <boojin.kim@samsung.com>,
	vinod.koul@intel.com, 'Jassi Brar' <jassisinghbrar@gmail.com>,
	'Grant Likely' <grant.likely@secretlab.ca>,
	'Kukjin Kim' <kgene.kim@samsung.com>,
	'Mark Brown' <broonie@opensource.wolfsonmicro.com>,
	'Dan Williams' <dan.j.williams@intel.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH V4 04/14] DMA: PL330: Add DMA_CYCLIC capability
Date: Mon, 25 Jul 2011 16:18:04 +0530	[thread overview]
Message-ID: <1311590884.29703.2.camel@vkoul-mobl4> (raw)
In-Reply-To: <20110725103629.GF9653@n2100.arm.linux.org.uk>

On Mon, 2011-07-25 at 11:36 +0100, Russell King - ARM Linux wrote:
> On Mon, Jul 25, 2011 at 07:31:45PM +0900, Boojin Kim wrote:
> > > On Mon, Jul 25, 2011 at 10:28:22AM +0900, Boojin Kim wrote:
> > > > +static void pl330_tasklet_cyclic(unsigned long data)
> > > > +{
> > > > +	struct dma_pl330_chan *pch = (struct dma_pl330_chan *)data;
> > > > +	struct dma_pl330_desc *desc, *_dt;
> > > > +	unsigned long flags;
> > > > +	LIST_HEAD(list);
> > > > +
> > > > +	spin_lock_irqsave(&pch->lock, flags);
> > > ...
> > > > +			callback = desc->txd.callback;
> > > > +			if (callback)
> > > > +				callback(desc->txd.callback_param);
> > >
> > > On this again - what if the callback wants to terminate the DMA activity
> > > because there's no more audio data to be sent/received from the device?
> > 
> > Do you mean what is happened if the callback() is called after channel is
> > terminated ?
> > Or What is happened if Callback() calls 'dma_release_channel()' to terminate
> > DMA?
> 
> No.  I mean what if the callback wants to call dmaengine_terminate_all().
you are supposed to drop the lock here, that way callback can call any
DMA API, otherwise it will result in deadlock.
This make me wonder you haven't read the documentation at all, please
ensure you have read Documentation/dmaengine.txt before next posting
> 
> > > > +	if (!pch->cyclic_task) {
> > > > +		pch->cyclic_task =
> > > > +			kmalloc(sizeof(struct tasklet_struct), GFP_KERNEL);
> > > > +		tasklet_init(pch->cyclic_task,
> > > > +			pl330_tasklet_cyclic, (unsigned int)pch);
> > >
> > > Here you allocate memory for the cyclic task.  Above you set this pointer
> > > to NULL.  That sounds like a memory leak to me.  Why are you kmallocing
> > > this memory - why can't it be part of the dma_pl330_chan structure?  It's
> > > only 28 bytes.
> > 
> > It's my mistake. I should have been free of the memory.
> > 
> > And the reason why I use kmalloc for 'cyclic_task' is following.
> > This memory size for 'cyclic_tasklet' is the 896 bytes ( = the number of
> > channel * sizeof(struct tasklet_struct)= 32*28) for each DMAC. And This
> > memory size is increased according to the number of DMAC.
> > And Samsung has the DMAC that is dedicated for Mem-to-Mem operation. If I
> > make 'cyclic_task' be part of dma_pl330_chan, this DMAC that is dedicated
> > for Mem-to-Mem operation should hold unused data.
> > So, I think it's loss that all dma channels hold own 'cyclic_task'.
> 
> Could you re-use the tasklet that already exists?


-- 
~Vinod Koul
Intel Corp.