linux-kernel - Re: [BUG] dma-mapping: remove CONFIG_DMA

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Date:   Tue, 21 Jun 2022 10:31:54 -0400
From:   Mark Hounschell <markh@...pro.net>
To:     Christoph Hellwig <hch@....de>
Cc:     Robin Murphy <robin.murphy@....com>,
        Linux-kernel <linux-kernel@...r.kernel.org>,
        dmaengine@...r.kernel.org
Subject: Re: [BUG] dma-mapping: remove CONFIG_DMA_REMAP

On 6/21/22 10:19, Christoph Hellwig wrote:
> On Tue, Jun 21, 2022 at 10:06:59AM -0400, Mark Hounschell wrote:
>> On 6/21/22 09:48, Christoph Hellwig wrote:
>>> On Tue, Jun 21, 2022 at 09:43:18AM -0400, Mark Hounschell wrote:
>>>> Revert that commit and all works like normal. This commit breaks user land.
>>>
>>> No.  We had that discussion before.  It exposeѕ how broken your out of
>>> tree driver is, which you don't bother to fix despite Robin even taking
>>> the pains to explain you how.
>>
>> No, this is not the original issue and we never actually had a discussion.
>> That original issue was about using Set/ClearPageReserved. You nor Robin
>> even tried to explain why it was wrong to use it. It was never an issue in
>> previous kernels. Why now? In any case I have removed that code. This is
>> what happens now.
>>
>> What is it you think I am doing wrong. Except for using
>> Set/ClearPageReserved you have not explained anything to me.
> 
> Which part of "you must not call virt_to_page on the result that is
> very clearly stated in the documentation and has been explained to
> you repeatly" is still not clear to you?
> 

That has not been explained to me at all. I am NOT any longer using 
virt_to_page at all anywhere in the driver. I was told that 
Set/ClearPageReserve was what I was doing wrong. Not that I was using 
virt_to_page with it. I am not using either now. I am using only 
dma_alloc_coherent.

> Which part of "if your of tree modules stops working, this does not
> constitute userspace breakage" is not clear to you?
> 
> I'm done with this, please stop bothering me.

I am not trying to bother you and there is no reason for you to be rude 
to me. I just think this is a bug and am trying to get to the bottom of it.

Regards
Mark