linux-kernel - Re: [PATCH 2/2] usb: cdns3: Optimize DMA request buffer allocation

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Date:   Tue, 9 Mar 2021 09:28:04 +0000
From:   Christoph Hellwig <hch@...radead.org>
To:     Sanket Parmar <sparmar@...ence.com>
Cc:     peter.chen@...nel.org, pawell@...ence.com, a-govindraju@...com,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        kurahul@...ence.com, gregkh@...uxfoundation.org, kishon@...com
Subject: Re: [PATCH 2/2] usb: cdns3: Optimize DMA request buffer allocation

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.