Re: [RFC PATCH v3 2/6] swiotlb: Add restricted DMA pool

[Florian Fainelli <f.fainelli@gmail.com>]

On 1/5/21 7:41 PM, Claire Chang wrote:
> Add the initialization function to create restricted DMA pools from
> matching reserved-memory nodes in the device tree.
> 
> Signed-off-by: Claire Chang <tientzu@chromium.org>
> ---
>  include/linux/device.h  |   4 ++
>  include/linux/swiotlb.h |   7 +-
>  kernel/dma/Kconfig      |   1 +
>  kernel/dma/swiotlb.c    | 144 ++++++++++++++++++++++++++++++++++------
>  4 files changed, 131 insertions(+), 25 deletions(-)
> 
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 89bb8b84173e..ca6f71ec8871 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -413,6 +413,7 @@ struct dev_links_info {
>   * @dma_pools:	Dma pools (if dma'ble device).
>   * @dma_mem:	Internal for coherent mem override.
>   * @cma_area:	Contiguous memory area for dma allocations
> + * @dma_io_tlb_mem: Internal for swiotlb io_tlb_mem override.
>   * @archdata:	For arch-specific additions.
>   * @of_node:	Associated device tree node.
>   * @fwnode:	Associated device node supplied by platform firmware.
> @@ -515,6 +516,9 @@ struct device {
>  #ifdef CONFIG_DMA_CMA
>  	struct cma *cma_area;		/* contiguous memory area for dma
>  					   allocations */
> +#endif
> +#ifdef CONFIG_SWIOTLB
> +	struct io_tlb_mem	*dma_io_tlb_mem;
>  #endif
>  	/* arch specific additions */
>  	struct dev_archdata	archdata;
> diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
> index dd8eb57cbb8f..a1bbd7788885 100644
> --- a/include/linux/swiotlb.h
> +++ b/include/linux/swiotlb.h
> @@ -76,12 +76,13 @@ extern enum swiotlb_force swiotlb_force;
>   *
>   * @start:	The start address of the swiotlb memory pool. Used to do a quick
>   *		range check to see if the memory was in fact allocated by this
> - *		API.
> + *		API. For restricted DMA pool, this is device tree adjustable.

Maybe write it as this is "firmware adjustable" such that when/if ACPI
needs something like this, the description does not need updating.

[snip]

> +static int rmem_swiotlb_device_init(struct reserved_mem *rmem,
> +				    struct device *dev)
> +{
> +	struct io_tlb_mem *mem = rmem->priv;
> +	int ret;
> +
> +	if (dev->dma_io_tlb_mem)
> +		return -EBUSY;
> +
> +	if (!mem) {
> +		mem = kzalloc(sizeof(*mem), GFP_KERNEL);
> +		if (!mem)
> +			return -ENOMEM;
> +
> +		if (!memremap(rmem->base, rmem->size, MEMREMAP_WB)) {

MEMREMAP_WB sounds appropriate as a default.
Documentation/devicetree/bindings/reserved-memory/ramoops.txt does
define an "unbuffered" property which in premise could be applied to the
generic reserved memory binding as well and that we may have to be
honoring here, if we were to make it more generic. Oh well, this does
not need to be addressed right now I guess.
-- 
Florian