linux-kernel - Re: [PATCH] pch_dma: Fix suspend issue

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Message-ID: <1317968080.1573.2266.camel@vkoul-udesk3>
Date:	Fri, 07 Oct 2011 11:44:40 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Tomoya MORINAGA <tomoya-linux@....lapis-semi.com>
Cc:	Dan Williams <dan.j.williams@...el.com>,
	linux-kernel@...r.kernel.org, qi.wang@...el.com,
	yong.y.wang@...el.com, joel.clark@...el.com, kok.howg.ewe@...el.com
Subject: Re: [PATCH] pch_dma: Fix suspend issue

On Fri, 2011-10-07 at 14:54 +0900, Tomoya MORINAGA wrote:
> (2011/10/07 14:00), Vinod Koul wrote:
> > How would changing the max number of descriptors fix the memory
> > violation?
> >
> 
> In probe of pch_dma,  you can see the following code.
> 
> 	for (i = 0; i < nr_channels; i++) {
> 
> snip...
> 
> 		pd_chan->membase = &regs->desc[i];
> 
> snip...
> 
> 	}
> 
> Max value of nr_channels is 12 defined at pci_table.
> So, this caused memory access violation.
This is all is due to not saving nr_channels in probe and using that
instead.

Looking deeper, struct pch_dma defines array of length MAX_CHAN_NR for
channels. Then why do you allocate memory in probe as 
         pd = kzalloc(sizeof(struct pch_dma)+
                 sizeof(struct pch_dma_chan) * nr_channels, GFP_KERNEL);
what is the point in allocating additional memory for each channel?

Given this, why should there be predefined channel array in pcm_dma?

It would be great if we could fix this by dynamically allocating memory
for channels based on nr_channels and not wasting due to a static array.

-- 
~Vinod

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