linux-kernel - Re: [PATCH] i2c: ismt: fix wrong device address when unmap the data buffer

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Date:   Mon, 12 Jun 2017 13:29:15 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Peter Rosin <peda@...ntia.se>
Cc:     Song liwei <liwei.song@...driver.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        Seth Heasley <seth.heasley@...el.com>,
        Neil Horman <nhorman@...driver.com>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] i2c: ismt: fix wrong device address when unmap the data buffer

On Mon, Jun 12, 2017 at 1:19 PM, Peter Rosin <peda@...ntia.se> wrote:
> On 2017-06-12 11:38, Andy Shevchenko wrote:
>> On Mon, Jun 12, 2017 at 12:28 PM, Peter Rosin <peda@...ntia.se> wrote:
>>> On 2017-06-12 11:11, Andy Shevchenko wrote:
>>>> On Mon, Jun 12, 2017 at 6:42 AM, Song liwei <liwei.song@...driver.com> wrote:
>>>>> From: Liwei Song <liwei.song@...driver.com>
>>
>>>>> After finished I2C block read/write, when unmap the data buffer,
>>>>> a wrong device address was pass to dma_unmap_single(),
>>
>>>>> the right
>>>>> device address should be "dev" not "&adap->dev", the relation is
>>>>> *(&adap->dev) == dev.
>>>>
>>>> This is confusing. You are telling that there are two copies of struct
>>>> device here?
>>>
>>> Yes, there are two copies.
>>
>> No, there is not. See below.
>
> What I meant was that there are the struct device in pci_dev->dev and the
> struct device in adap->dev. That seems like two copies of struct device
> to me.

They are not copies. That's my point.

> I didn't mean that they are copies in the sense that they have the
> same content, but in the sense that they are both struct device.
>
> I guess we can argue ourselves blue over this point.

See above.

>> There are two struct devices,
>
> Hmm, two struct devices, I seem to recall that from somewhere... :-)

Okay, it's possible bad wording from my side.

>>                               one is a real PCI device, which
>> represents actual device what *does* DMA.
>> This struct should be used according to DMA API.

> When you put it like that, it's obvious that the patch is correct.

I agreed with this in the first place! See my first reply.

>  I had
> this feeling that little thought had gone into the choice to pick "dev"
> over "&adap->dev", that's all.

As I said, my concern is the commit message to the change which is
totally confusing.

-- 
With Best Regards,
Andy Shevchenko