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

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Message-ID: <1364202254.18714.101.camel@smile>
Date:	Mon, 25 Mar 2013 11:04:14 +0200
From:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:	Arnd Bergmann <arnd@...db.de>
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 Fri, 2013-03-22 at 15:19 +0000, Arnd Bergmann wrote: 
> 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.

Right.


> 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.

I don't. For checking we have special make targets:

  allnoconfig     - New config where all options are answered with no
  allyesconfig    - New config where all options are accepted with yes
  allmodconfig    - New config selecting modules when possible
  alldefconfig    - New config with all symbols set to default

> > -	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.

Actually to be aligned with other dmaengine code it should return
-ENOSYS. And by description ENOSYS seems  suitable for "not implemented"
cases.


What about to move all CONFIG_OF stuff into separate file?


-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy
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