linux-kernel - Re: [PATCH v2 2/3] i2c: Add helper to ease DMA handling

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Date:   Thu, 9 Aug 2018 17:13:20 +0800
From:   Yingjoe Chen <yingjoe.chen@...iatek.com>
To:     Wolfram Sang <wsa@...-dreams.de>
CC:     Jun Gao <jun.gao@...iatek.com>, <devicetree@...r.kernel.org>,
        <srv_heupstream@...iatek.com>, <linux-kernel@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>, <linux-i2c@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 2/3] i2c: Add helper to ease DMA handling

On Wed, 2018-08-08 at 22:57 +0200, Wolfram Sang wrote:
> On Sat, Jul 07, 2018 at 05:29:54PM +0800, Jun Gao wrote:
> > From: Jun Gao <jun.gao@...iatek.com>
> > 
> > This function is needed by i2c_get_dma_safe_msg_buf() potentially.
> > It is used to free DMA safe buffer when DMA operation fails.
> > 
> > Signed-off-by: Jun Gao <jun.gao@...iatek.com>
> 
> Right, we need something like this. This leaks in the sh_mobile driver,
> too :(
> 
> I am still thinking if there is a nice way to put this functionality
> into i2c_release_dma_safe_msg_buf() itself somehow...

Wolfram,

I have second thought on these API now. Recently, we have saw similar
issue for spi device driver.

I believe the reason for these api is because some arch changed to can
not do DMA on stack recently. Maybe we should have dma_mapping to bounce
buffer like it bounce un-dma-able address for those arch? or we should
have a common driver API for this, not just for i2c?

Joe.C