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From:   Sanket Parmar <sparmar@cadence.com>
To:     Christoph Hellwig <hch@infradead.org>
CC:     "peter.chen@kernel.org" <peter.chen@kernel.org>,
        Pawel Laszczak <pawell@cadence.com>,
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        Rahul Kumar <kurahul@cadence.com>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        "kishon@ti.com" <kishon@ti.com>
Subject: RE: [PATCH 2/2] usb: cdns3: Optimize DMA request buffer allocation
Thread-Topic: [PATCH 2/2] usb: cdns3: Optimize DMA request buffer allocation
Thread-Index: AQHXFKPlwE5egmmpm02b66W+ylYqvKp7Y7sAgAAIZFCAAAlEAIAABGcQ
Date:   Tue, 9 Mar 2021 10:49:27 +0000
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> On Tue, Mar 09, 2021 at 10:18:43AM +0000, Sanket Parmar wrote:
> > > On Tue, Mar 09, 2021 at 06:19:40AM +0100, Sanket Parmar wrote:
> > > > dma_alloc_coherent() might fail on the platform with a small DMA
> region.
> > > >
> > > > To avoid such failure in cdns3_prepare_aligned_request_buf(),
> > > > dma_alloc_coherent() is replaced with kmalloc and dma_map API to
> > > > allocate aligned request buffer of dynamic length.
> > >
> > > dma_alloc_noncoherent is the proper API instead of using kmalloc, whi=
ch
> > > can lead to unaddressable memory that might require bounce buffering.
> >
> > cdns3 device required DMA coherent buffer to perform operations. So
> > dma_alloc_noncoherent will not help here.
> >
> > Also all gadget classes(except g_ether) use kmalloc to allocated reques=
t
> buffer,
> > and device driver uses usb_gadget_map_request_by_dev to map the
> request
> > buffer. Similar approach is used to allocate aligned buffer.
>=20
> If you can use kmalloc and dma_map_single you can use
> dma_alloc_noncoherent per definition.

Okay. I was not aware of it. I will test it.=20
Thank you for your feedback.

--
Sanket