RE: [PATCH 2/2] usb: cdns3: Optimize DMA request buffer allocation

[Sanket Parmar]

> 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, which
> > > 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 request
> buffer,
> > and device driver uses usb_gadget_map_request_by_dev to map the
> request
> > buffer. Similar approach is used to allocate aligned buffer.
> 
> 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. 
Thank you for your feedback.

--
Sanket