linux-kernel - Re: [PATCH 09/15] device core: Add ability to handle multiple dma offsets

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Message-ID: <20200520054349.GB2180554@kroah.com>
Date:   Wed, 20 May 2020 07:43:49 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Jim Quinlan <james.quinlan@...adcom.com>
Cc:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Saravana Kannan <saravanak@...gle.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:DMA MAPPING HELPERS" <iommu@...ts.linux-foundation.org>
Subject: Re: [PATCH 09/15] device core: Add ability to handle multiple dma
 offsets

On Tue, May 19, 2020 at 04:34:07PM -0400, Jim Quinlan wrote:
> diff --git a/include/linux/device.h b/include/linux/device.h
> index ac8e37cd716a..6cd916860b5f 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -493,6 +493,8 @@ struct dev_links_info {
>   * @bus_dma_limit: Limit of an upstream bridge or bus which imposes a smaller
>   *		DMA limit than the device itself supports.
>   * @dma_pfn_offset: offset of DMA memory range relatively of RAM
> + * @dma_map:	Like dma_pfn_offset but used when there are multiple
> + *		pfn offsets for multiple dma-ranges.
>   * @dma_parms:	A low level driver may set these to teach IOMMU code about
>   * 		segment limitations.
>   * @dma_pools:	Dma pools (if dma'ble device).
> @@ -578,7 +580,12 @@ struct device {
>  					     allocations such descriptors. */
>  	u64		bus_dma_limit;	/* upstream dma constraint */
>  	unsigned long	dma_pfn_offset;
> -
> +#ifdef CONFIG_DMA_PFN_OFFSET_MAP
> +	const void *dma_offset_map;	/* Like dma_pfn_offset, but for
> +					 * the unlikely case of multiple
> +					 * offsets. If non-null, dma_pfn_offset
> +					 * will be 0. */
> +#endif
>  	struct device_dma_parameters *dma_parms;
>  
>  	struct list_head	dma_pools;	/* dma pools (if dma'ble) */

I'll defer to Christoph here, but I thought we were trying to get rid of
stuff like this from struct device, not add new things to it for dma
apis.  And why is it a void *?

thanks,

greg k-h