linux-kernel - Re: [PATCH] m32r: add simple dma

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Date:   Sun, 30 Oct 2016 23:47:29 +0530
From:   Sudip Mukherjee <sudipm.mukherjee@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     linux-kernel@...r.kernel.org, fengguang.wu@...el.com
Subject: Re: [PATCH] m32r: add simple dma

Hi Andrew,

On Friday 21 October 2016 08:59 AM, Andrew Morton wrote:
> On Sat,  8 Oct 2016 23:23:18 +0530 Sudip Mukherjee <sudipm.mukherjee@...il.com> wrote:
>
>> Some builds of m32r were failing as it tried to build few drivers which
>> needed dma but m32r is not having dma support. Objections were raised
>> when it was tried to make those drivers depend on HAS_DMA.
>
> Huh.  What were these objections?  That sounds like the appropriate
> fix.  And I suggest that a summary of those objections be captured in
> this patch's changelog.

Sorry for the delay in reply. Got busy in dayjob and relocation.

I was asked to provide dma stubs instead of adding HAS_DMA in the Kconfig.

http://www.spinics.net/lists/kernel/msg2277152.html

And an old thread-
http://www.spinics.net/lists/alsa-devel/msg50931.html

It appeared to me that instead of adding dma stubs and returning error 
values from them it will be better to add dma_noop to m32r. Looking at 
the simplicity of dma_noop it seems that it should work.
What will you suggest? Do i send v2 after adding the "dma stub" comment 
and the link to the thread in the commit message or should I opt for dma 
stub?

>
>> So the next
>> best thing is to add dma support to m32r.
>> dma_noop is a very simple dma with 1:1 memory mapping.
>>
>> Signed-off-by: Sudip Mukherjee <sudip.mukherjee@...ethink.co.uk>
>> ---
>>
>> Hi Andrew,
>> Just to let you know that this was not tested on any board. I think I
>> have told you earlier that inspite of all  my efforts I could not find
>>   any source of information to procure a board of m32r.
>
> It is a worry.  We're saying "m32r linux now supports these drivers",
> only we don't know if that is true.

FYI, I tried to contact Renesas for m32r boards and this is the reply I 
received (Dated- Jan 20, 2016):
"
Hi Sudip-san,
I’m afraid but I don’t know about m32r.
Also I searched our private web site, I could not find usuful 
information about m32r…
Best regards,
Yoshihiro Shimoda
"

Regards
Sudip