linux-kernel - Re: [PATCH 3/4] dw_dmac: make build of DT related methods optional

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Date:	Fri, 22 Mar 2013 15:19:13 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:	Vinod Koul <vinod.koul@...el.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	linux-kernel@...r.kernel.org,
	"spear-devel" <spear-devel@...t.st.com>
Subject: Re: [PATCH 3/4] dw_dmac: make build of DT related methods optional

On Friday 22 March 2013, Andy Shevchenko wrote:
> There is no reason to build custom filter function and translation function
> inside the driver in case we have no DT platform.
> 
> This patch introduces new method dw_dma_of_controller_register() and moves all
> DT related stuff under #ifdef CONFIG_OF. It also helps to distinguish the real
> -ENODEV return code of fake one when of_dma_controller_register is not
> implemented.
> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

This should have no impact on the object code at all, since everything
inside of the #ifdef is be dropped by the compiler anyway if
of_dma_controller_register is stubbed out.

I generally prefer to have all driver code be compiled  all the time
to catch build regressions independent of the configuration, and leave
the #ifdefs in header files that provide the interfaces.

> -	if (pdev->dev.of_node) {
> -		err = of_dma_controller_register(pdev->dev.of_node,
> -						 dw_dma_of_xlate, dw);
> -		if (err && err != -ENODEV)
> -			dev_err(&pdev->dev,
> -				"could not register of_dma_controller\n");
> -	}
> +	if (pdev->dev.of_node)
> +		dw_dma_of_controller_register(dw);

If you want to remove the "err != -ENODEV" check here, we could rewrite
this as 

	if (IS_ENABLED(CONFIG_OF)) && pdev->dev.of_node) {
		err = of_dma_controller_register(pdev->dev.of_node,
						 dw_dma_of_xlate, dw);
		if (err)
			dev_err(&pdev->dev,
				"could not register of_dma_controller\n");
	}

Or alternatively, we can change the of_dma_controller_register() stub to
return 0 if CONFIG_OF is disabled. That would also take care of similar
code in other dma engine drivers.

	Arnd
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