linux-kernel - Re: Cma mem map to cpu address when allocated in ion driver, why do this design?

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Message-ID: <20160901144530.GC11190@kroah.com>
Date:   Thu, 1 Sep 2016 16:45:30 +0200
From:   "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:     "Yangwei (Yang Wei, Device Chipset Key Technologies Platform Development
        Dept)" <yyangwei.yangwei@...ilicon.com>
Cc:     "labbott@...hat.com" <labbott@...hat.com>,
        "sumit.semwal@...aro.org" <sumit.semwal@...aro.org>,
        "arve@...roid.com" <arve@...roid.com>,
        "riandrews@...roid.com" <riandrews@...roid.com>,
        "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Zengtao (B)" <prime.zeng@...ilicon.com>,
        "Chenhao (benjamin)" <benjamin.chenhao@...ilicon.com>
Subject: Re: Cma mem map to cpu address when allocated in ion driver, why do
 this design?

On Thu, Sep 01, 2016 at 12:46:32PM +0000, Yangwei (Yang Wei, Device Chipset Key Technologies Platform Development Dept) wrote:
> Hi  all,
> 
> When I review ion code in linux-3.18.y, I find a design that may cause
> a problem in our product. In the design, cma mem is allocated via the
> interface of dma_alloc_coherent ,

3.18 is old and obsolete and isn't supported by the kernel community for
anything except bug fixes.  I suggest you work with whatever group is
forcing you to use this old kernel version as they are the ones that you
are paying to support this kernel for you.

If you wish to discuss the 4.7 or newer kernel versions, and how ion
works there (look in linux-next for the most recent changes in that
area), we would be glad to help you out.

Best of luck!

greg k-h