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Message-ID: <jrsw27uoc3wo7b7ry4mgkak2feyrvznad2b2pbmr3coabpulgy@lyfkfj3oik5l>
Date: Mon, 30 Jun 2025 15:26:26 +0800
From: Xu Yang <xu.yang_2@....com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: ezequiel@...guardiasur.com.ar, mchehab@...nel.org,
laurent.pinchart@...asonboard.com, hdegoede@...hat.com, gregkh@...uxfoundation.org,
mingo@...nel.org, tglx@...utronix.de, viro@...iv.linux.org.uk,
thomas.weissschuh@...utronix.de, linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-usb@...r.kernel.org, imx@...ts.linux.dev, jun.li@....com
Subject: Re: [PATCH v2 1/3] usb: core: add dma-noncoherent buffer alloc and
free API
Hi Andy,
Thanks for your comments!
On Fri, Jun 27, 2025 at 02:22:59PM +0300, Andy Shevchenko wrote:
> On Fri, Jun 27, 2025 at 06:19:37PM +0800, Xu Yang wrote:
> > This will add usb_alloc_noncoherent() and usb_free_noncoherent()
> > functions to support alloc and free buffer in a dma-noncoherent way.
> >
> > To explicit manage the memory ownership for the kernel and device,
> > this will also add usb_dma_noncoherent_sync_for_cpu/device() functions
> > and call it at proper time. The management requires the user save
> > sg_table returned by usb_alloc_noncoherent() to urb->sgt.
>
> ...
>
> > +/**
> > + * usb_alloc_noncoherent - allocate dma-noncoherent buffer for URB_NO_xxx_DMA_MAP
> > + * @dev: device the buffer will be used with
> > + * @size: requested buffer size
> > + * @mem_flags: affect whether allocation may block
> > + * @dma: used to return DMA address of buffer
> > + * @dir: dma transfer direction
> > + * @table: used to return sg_table of allocated memory
> > + *
> > + * Return: Either null (indicating no buffer could be allocated), or the
> > + * cpu-space pointer to a buffer that may be used to perform DMA to the
> > + * specified device. Such cpu-space buffers are returned along with the DMA
> > + * address (through the pointer provided).
>
> Return section should be last in the kernel-doc (this requirement is
> documented).
Okay. I'll improve it.
>
> > + * To explicit manage the memory ownership for the kernel vs the device by
> > + * usb core, the user needs save sg_table to urb->sgt. Then usb core will
> > + * do dma sync for cpu and device properly.
> > + *
> > + * When the buffer is no longer used, free it with usb_free_noncoherent().
>
> Here and everywhere else in your series, pay respect to acronyms by using them
> as acronyms:
>
> dma --> DMA
> cpu --> CPU
> usb --> USB
>
> and so on...
Okay.
>
>
> > + */
> > +void *usb_alloc_noncoherent(struct usb_device *dev, size_t size,
> > + gfp_t mem_flags, dma_addr_t *dma,
> > + enum dma_data_direction dir,
> > + struct sg_table **table)
> > +{
> > + struct device *dmadev;
> > + struct sg_table *sgt;
> > + void *buffer;
> > +
> > + if (!dev || !dev->bus)
>
> When !dev case is possible?
Not exactly sure, but it depends on the user. This sanity test is also
carried over from usb_alloc_coherent() to avoid any surprise.
>
> > + return NULL;
> > +
> > + dmadev = bus_to_hcd(dev->bus)->self.sysdev;
> > +
> > + sgt = dma_alloc_noncontiguous(dmadev, size, dir, mem_flags, 0);
> > + if (!sgt)
> > + return NULL;
> > +
> > + buffer = dma_vmap_noncontiguous(dmadev, size, sgt);
> > + if (!buffer) {
> > + dma_free_noncontiguous(dmadev, size, sgt, dir);
> > + return NULL;
> > + }
> > +
> > + *table = sgt;
> > + *dma = sg_dma_address(sgt->sgl);
> > +
> > + return buffer;
> > +}
>
> ...
>
> > +void usb_free_noncoherent(struct usb_device *dev, size_t size,
> > + void *addr, enum dma_data_direction dir,
> > + struct sg_table *table)
> > +{
> > + struct device *dmadev;
> > +
> > + if (!dev || !dev->bus)
>
> Ditto.
>
> > + return;
> > + if (!addr)
> > + return;
> > +
> > + dmadev = bus_to_hcd(dev->bus)->self.sysdev;
> > + dma_vunmap_noncontiguous(dmadev, addr);
> > + dma_free_noncontiguous(dmadev, size, table, dir);
> > +}
Thanks,
Xu Yang
>
> --
> With Best Regards,
> Andy Shevchenko
>
>
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