linux-kernel - Re: [PATCH 13/32] dmaengine: ste_dma40: Calculate number of logical channels from physical ones

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Message-ID: <20130425092930.GI4623@gmail.com>
Date:	Thu, 25 Apr 2013 10:29:30 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Linus WALLEIJ <linus.walleij@...ricsson.com>,
	Vinod Koul <vinod.koul@...el.com>, Dan Williams <djbw@...com>,
	Per Forlin <per.forlin@...ricsson.com>,
	Rabin Vincent <rabin@....in>
Subject: Re: [PATCH 13/32] dmaengine: ste_dma40: Calculate number of logical
 channels from physical ones

On Thu, 25 Apr 2013, Linus Walleij wrote:

> On Thu, Apr 18, 2013 at 12:11 PM, Lee Jones <lee.jones@...aro.org> wrote:
> 
> > This change will cost ~25KB of memory, but it's worth the trade-off,
> > as it removes a great deal of overhead. It means that instead of only
> > allocating memory for the logical channels in use, it does so for all
> > available ones, which is 32 per physical channel. However, this now
> > means we can remove some platform data and we don't have to worry
> > about adding vendor specific variables to Device Tree.
> >
> > Cc: Vinod Koul <vinod.koul@...el.com>
> > Cc: Dan Williams <djbw@...com>
> > Cc: Per Forlin <per.forlin@...ricsson.com>
> > Cc: Rabin Vincent <rabin@....in>
> > Signed-off-by: Lee Jones <lee.jones@...aro.org>
> 
> (...)
> >  static struct stedma40_platform_data dma40_plat_data = {
> > -       .dev_len = DB8500_DMA_NR_DEV,
> 
> So that was set to 64 in the platform...
> 
> > -       /* Count the number of logical channels in use */
> > -       for (i = 0; i < plat_data->dev_len; i++)
> > -               if (plat_data->dev_rx[i] != 0)
> > -                       num_log_chans++;
> > -
> > -       for (i = 0; i < plat_data->dev_len; i++)
> > -               if (plat_data->dev_tx[i] != 0)
> > -                       num_log_chans++;
> 
> And I guess this code snippet made it go down to <= 32 all the time,
> correct?

However many were described in dma40_[rx|tx]_map, yes.

> Just want to understand it before I ACK. (The idea is sound.)
> 
> I notice there is no check whatsoever of the bounds of
> plat_data->dev_[rx|tx]  but that is a different problem I guess...

The array is going away anyway, so we don't need to threat.

-- 
Lee Jones
Linaro ST-Ericsson Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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