linux-kernel - Re: [PATCH 2/2] dma: of: Remove check on always true condition

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Date:	Mon, 22 Apr 2013 15:52:39 -0500
From:	Jon Hunter <jon-hunter@...com>
To:	Lars-Peter Clausen <lars@...afoo.de>
CC:	Vinod Koul <vinod.koul@...el.com>, Arnd Bergmann <arnd@...db.de>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] dma: of: Remove check on always true condition


On 04/22/2013 03:33 AM, Lars-Peter Clausen wrote:
> Both of_dma_nbcells field of the of_dma_controller and the args_count field of
> the dma_spec are initialized by parsing the #dma-cells attribute of their device
> tree node. So if the device tree nodes of a DMA controller and the dma_spec
> match this means that of_dma_nbcells and args_count will also match. So the
> second test in the of_dma_find_controller loop is redundant because given the
> first test yields true the second test will also yield true. So we can safely
> remove the test whether of_dma_nbcells matches args_count. Since this was the
> last user of the of_dma_nbcells field we can remove it altogether.

This assumes that someone has correctly added the dma information to the
dma slave binding. I could see systems where different dma controllers
have different of_dma_nbcells and so someone could put the enter wrong
number of cells for a dma slave binding. Its really to catch user error.

> Signed-off-by: Lars-Peter Clausen <lars@...afoo.de>
> ---
>  drivers/dma/of-dma.c   | 14 +-------------
>  include/linux/of_dma.h |  1 -
>  2 files changed, 1 insertion(+), 14 deletions(-)
> 
> diff --git a/drivers/dma/of-dma.c b/drivers/dma/of-dma.c
> index 268cc8a..75334bd 100644
> --- a/drivers/dma/of-dma.c
> +++ b/drivers/dma/of-dma.c
> @@ -35,8 +35,7 @@ static struct of_dma *of_dma_find_controller(struct of_phandle_args *dma_spec)
>  	struct of_dma *ofdma;
>  
>  	list_for_each_entry(ofdma, &of_dma_list, of_dma_controllers)
> -		if ((ofdma->of_node == dma_spec->np) &&
> -		    (ofdma->of_dma_nbcells == dma_spec->args_count))
> +		if (ofdma->of_node == dma_spec->np)
>  			return ofdma;

Other device-tree functions perform similar tests to this such as ...

static int of_gpiochip_find_and_xlate(struct gpio_chip *gc, void *data)
{
         struct gg_data *gg_data = data;
         int ret;

         if ((gc->of_node != gg_data->gpiospec.np) ||
             (gc->of_gpio_n_cells != gg_data->gpiospec.args_count) ||
             (!gc->of_xlate))
                 return false;

...

Cheers
Jon
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