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Message-ID: <aF5_EwSHHMOOMRv9@smile.fi.intel.com>
Date: Fri, 27 Jun 2025 14:22:59 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Xu Yang <xu.yang_2@....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
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).
> + * 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...
> + */
> +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?
> + 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);
> +}
--
With Best Regards,
Andy Shevchenko
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