linux-kernel - Re: [RFC PATCH v2 0/3] prerequisites for device reserved local mem rework

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Message-ID: <0e5f3b86-7a80-eec7-691b-34a123194208@nxp.com>
Date:   Wed, 15 May 2019 10:37:03 +0000
From:   Laurentiu Tudor <laurentiu.tudor@....com>
To:     Fredrik Noring <noring@...rew.org>,
        Robin Murphy <robin.murphy@....com>
CC:     "hch@....de" <hch@....de>,
        "stern@...land.harvard.edu" <stern@...land.harvard.edu>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "marex@...x.de" <marex@...x.de>,
        "JuergenUrban@....de" <JuergenUrban@....de>,
        Leo Li <leoyang.li@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v2 0/3] prerequisites for device reserved local mem
 rework

Hello,

On 14.05.2019 21:29, Fredrik Noring wrote:
> Thanks Robin!
> 
>>> For HCs that have local memory, replace the current DMA API usage
>>> with a genalloc generic allocator to manage the mappings for these
>>> devices.
>>> This is in preparation for dropping the existing "coherent" dma
>>> mem declaration APIs. Current implementation was relying on a short
>>> circuit in the DMA API that in the end, was acting as an allocator
>>> for these type of devices.
>>>
>>> Only compiled tested, so any volunteers willing to test are most welcome.
>>
>> I recall an out-of-tree PlayStation 2 OHCI driver being another
>> HCD_LOCAL_MEM user - if Fredrik and Juergen are still active on that,
>> hopefully they might be able to comment on whether this approach can
>> work for them too. Patchwork link just in case:
>> https://patchwork.kernel.org/project/linux-usb/list/?series=117433
> 
> True. In fact I'm preparing a patch submission for this PS2 OHCI driver,
> along with about a hundred other patches (unrelated to the USB subsystem).
> Hopefully in a few weeks. My patches are currently on top of v5.0. What
> branch/version is recommended to try this DMA update?

I think that any recent kernel will do, so I'd say your current branch 
should be fine.

> Here is the v5.0.11 PS2 OHCI driver, for reference:
> 
> https://github.com/frno7/linux/blob/ps2-v5.0.11/drivers/usb/host/ohci-ps2.c
Please note that the driver will need to be updated, see here for an 
example:

https://patchwork.kernel.org/patch/10943105/

---
Best Regards, Lauretniu