linux-kernel - Re: Please revert the addition of the AMD QDMA driver

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Message-ID: <4fe5374e-8eb2-9ff6-e2ea-e55342c59de6@amd.com>
Date: Mon, 16 Sep 2024 16:48:59 -0700
From: Lizhi Hou <lizhi.hou@....com>
To: Christoph Hellwig <hch@....de>, Vinod Koul <vkoul@...nel.org>, "Nishad
 Saraf" <nishads@....com>
CC: <dmaengine@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: Please revert the addition of the AMD QDMA driver

Hi Christoph and Vinod,


Sorry, I did not know the limitation of get/set_dma_ops.

Instead of reverting the entire driver, is it ok to put a fix on top to 
address this issue?


Thanks,

Lizhi

On 9/16/24 00:40, Christoph Hellwig wrote:
> Hi Vinod,
>
> I just noticed you added the AMD QDMA driver for this merge window,
> which is completely broken in terms of DMA API usage by using the
> private get/set_dma_ops APIs.  These were never for driver use (
> and I've been working for years to fix the few abusers), but with the
> DMA changes in 6.12 it actually can't work at all, as the dma-iommu
> driver now also sets NULL DMA ops in addition to dma-direct.
>
> As a reminder drivers must never try to inherit dma settings from
> one device or another, instead pass the actual DMA device to whatever
> layer does the DMA mapping.  Without that you break all kinds of
> thing.
>
>