Re: [PATCH v2] ARM: imx: fix error handling

[Emil Goode <emilgoode@gmail.com>]

Hello Uwe,

On Sat, May 17, 2014 at 09:05:46PM +0200, Uwe Kleine-König wrote:
> Hello Emil,
> 
> On Sat, May 17, 2014 at 05:35:40PM +0200, Emil Goode wrote:
> > On Fri, May 16, 2014 at 09:31:39PM +0200, Uwe Kleine-König wrote:
> > > On Fri, May 16, 2014 at 01:49:10PM +0200, walter harms wrote:
> > > > Am 16.05.2014 13:16, schrieb Emil Goode:
> > > > > Hello Walter,
> > > > > 
> > > > > On Fri, May 16, 2014 at 12:40:19PM +0200, walter harms wrote:
> > > > >>
> > > > >>
> > > > >> Am 16.05.2014 11:54, schrieb Emil Goode:
> > > > >>> If we fail to allocate struct platform_device pdev we
> > > > >>> dereference it after the goto label err.
> > > > >>>
> > > > >>> I have rearranged the error handling a bit to fix the issue
> > > > >>> and also make it more clear.
> > > > >>>
> > > > >>> Signed-off-by: Emil Goode <emilgoode@gmail.com>
> > > > >>> ---
> > > > >>> v2: Changed to return -ENOMEM instead of ret where possible and
> > > > >>>     updated the subject line.
> > > > >>>
> > > > >>>  arch/arm/mach-imx/devices/platform-ipu-core.c |   22 +++++++++++++---------
> > > > >>>  1 file changed, 13 insertions(+), 9 deletions(-)
> > > > >>>
> > > > >>> diff --git a/arch/arm/mach-imx/devices/platform-ipu-core.c b/arch/arm/mach-imx/devices/platform-ipu-core.c
> > > > >>> index fc4dd7c..68f2a4a 100644
> > > > >>> --- a/arch/arm/mach-imx/devices/platform-ipu-core.c
> > > > >>> +++ b/arch/arm/mach-imx/devices/platform-ipu-core.c
> > > > >>> @@ -77,34 +77,38 @@ struct platform_device *__init imx_alloc_mx3_camera(
> > > > >>>  
> > > > >>>  	pdev = platform_device_alloc("mx3-camera", 0);
> > > > >>>  	if (!pdev)
> > > > >>> -		goto err;
> > > > >>> +		return ERR_PTR(-ENOMEM);
> > > > >>>  
> > > > >>>  	pdev->dev.dma_mask = kmalloc(sizeof(*pdev->dev.dma_mask), GFP_KERNEL);
> > > > >>>  	if (!pdev->dev.dma_mask)
> > > > >>> -		goto err;
> > > > >>> +		goto put_pdev;
> > > > >>>  
> > > > >>>  	*pdev->dev.dma_mask = DMA_BIT_MASK(32);
> > > > >>>  	pdev->dev.coherent_dma_mask = DMA_BIT_MASK(32);
> > > > >>>  
> > > > >>>  	ret = platform_device_add_resources(pdev, res, ARRAY_SIZE(res));
> > > > >>>  	if (ret)
> > > > >>> -		goto err;
> > > > >>> +		goto free_dma_mask;
> > > > >>>  
> > > > >>>  	if (pdata) {
> > > > >>>  		struct mx3_camera_pdata *copied_pdata;
> > > > >>>  
> > > > >>>  		ret = platform_device_add_data(pdev, pdata, sizeof(*pdata));
> > > > >>> -		if (ret) {
> > > > >>> -err:
> > > > >>> -			kfree(pdev->dev.dma_mask);
> > > > >>> -			platform_device_put(pdev);
> > > > >>> -			return ERR_PTR(-ENODEV);
> > > > >>> -		}
> > > > >>> +		if (ret)
> > > > >>> +			goto free_dma_mask;
> > > > >>> +
> > > > >>>  		copied_pdata = dev_get_platdata(&pdev->dev);
> > > > >>>  		copied_pdata->dma_dev = &imx_ipu_coredev->dev;
> > > > >>
> > > > >>
> > > > >> the patch is fine, but what use is this copied_pdata ?
> > > > >> It scope ends next line ?
> > > > >>
> > > > >> re,
> > > > >>  wh
> > > > > 
> > > > > I also thought that looked a bit odd, but copied_pdata is a temporary
> > > > > pointer to platform_data of the dev struct.
> > > > > 
> > > > > dev_get_platdata looks like this:
> > > > > 
> > > > > static inline void *dev_get_platdata(const struct device *dev)
> > > > > {
> > > > >         return dev->platform_data;
> > > > > }
> > > > > 
> > > > > So I believe it's a more compact way of writing:
> > > > > 
> > > > > pdev->dev->platform_data->dma_dev = &imx_ipu_coredev->dev;
> > > It's not about compactness. The dev_get_platdata accessor exists to be
> > > used instead of directly accessing dev->platform_data. I admit a comment
> > > would be nice ...
> > > 
> > > Anyhow this is all ugly, actually you'd want to have the dma_dev member
> > > already fixed when calling platform_device_add_data. But you cannot
> > > simply do
> > > 
> > > 	pdata->dma_dev = &imx_ipu_coredev->dev;
> > > 	ret = platform_device_add_data(pdev, pdata, sizeof(*pdata));
> > > 
> > > because *pdata is const.
> > 
> > Thank you for the explanation. Regarding the possibility of using
> > platform_device_register_full() to simplify this function. It seem to
> > be possible, the following inline function is available to help with this.
> > 
> > imx_add_platform_device_dmamask()
> I'd prefer to use platform_device_register_full directly (and let the
> wrapper die).

Ok, will skip the wrapper.

> 
> > But as you mentioned above we need to allocate a new platform_device
> > struct before we can assign &imx_ipu_coredev->dev to dma_dev, since
> > pdata is const. I guess this assignment could be done after calling
> > imx_add_platform_device_dmamask() but I don't think that makes the
> No, that won't work, because after platform_device_register_full returns
> you must assume that the device is already bound by a driver. And then
> you must not change platform_data anymore.

I see, thanks for explaining.

> 
> The only thing that would work is:
> 
> 	struct mx3_camera_pdata tmppdata;
> 
> 	if (pdata) {
> 		tmppdata = *pdata;
> 		tmppdata.dma_dev = &imx_ipu_coredev->dev;
> 
> 		pdata = &tmppdata;
> 	}
> 
> 	platform_device_register_full(... pdata ...)

You are right, that would work.

Will look at this again tomorrow.

Thank you!

Best regards,

Emil Goode