linux-kernel - Re: [PATCH] mfd: inherit coherent_dma

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Date:	Mon, 22 Sep 2014 21:45:40 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Boris BREZILLON <boris.brezillon@...e-electrons.com>
Cc:	Samuel Ortiz <sameo@...ux.intel.com>,
	Lee Jones <lee.jones@...aro.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mfd: inherit coherent_dma_mask from parent device

On Monday 22 September 2014 21:37:55 Boris BREZILLON wrote:
> dma_mask and dma_parms are already inherited from the parent device but
> dma_coherent_mask was left uninitialized (set to zero thanks to kzalloc).
> Set sub-device coherent_dma_mask to its parent value to simplify
> sub-drivers making use of dma coherent helper functions (those drivers
> currently have to explicitly set the dma coherent mask using
> dma_set_coherent_mask function).
> 
> Signed-off-by: Boris BREZILLON <boris.brezillon@...e-electrons.com>
> ---
> 
> Hi,
> 
> This patch is follow-up of a discussion we had on a KMS driver thread [1].
> This patch is only copying the parent device coherent_dma_mask to avoid
> calling specific dma_set_coherent_mask in case the coherent mask is the
> default one.
> 
> I'm a bit surprised this hasn't been done earlier while other dma fields
> (mask and parms) are already inherited from the parent device, so please
> tell me if there already was an attempt to do the same, and if so, what
> was the reson for rejecting it :-).
> 
> 

Seems reasonable to me. It's not clear whether we should always inherit
the dma_mask, but I see no point in copying just dma_mask but not
coherent_dma_mask.

Acked-by: Arnd Bergmann <arnd@...db.de>
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