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Subject: Re: [PATCH] dma-contiguous: CMA: give precedence to cmdline
To:     Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
        Christoph Hellwig <hch@lst.de>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Robin Murphy <robin.murphy@arm.com>
Cc:     iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org
References: <20200110171933.15014-1-nsaenzjulienne@suse.de>
From:   Phil Elwell <phil@raspberrypi.org>
Message-ID: <7ae5bad5-eee6-407f-bfa1-aff34f1a0550@raspberrypi.org>
Date:   Fri, 10 Jan 2020 17:36:30 +0000
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Hi Nicolas,

On 10/01/2020 17:19, Nicolas Saenz Julienne wrote:
> Although the device tree might contain a reserved-memory DT node
> dedicated as the default CMA pool, users might want to change CMA's
> parameters using the kernel command line for debugging purposes and
> whatnot. Honor this by bypassing the reserved memory CMA setup, which
> will ultimately end up freeing the memblock and allow the command line
> CMA configuration routine to run.
> 
> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
> ---
> 
> NOTE: Tested this on arm and arm64 with the Raspberry Pi 4.
> 
>   kernel/dma/contiguous.c | 9 ++++++++-
>   1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
> index daa4e6eefdde..8bc6f2d670f9 100644
> --- a/kernel/dma/contiguous.c
> +++ b/kernel/dma/contiguous.c
> @@ -302,9 +302,16 @@ static int __init rmem_cma_setup(struct reserved_mem *rmem)
>   	phys_addr_t align = PAGE_SIZE << max(MAX_ORDER - 1, pageblock_order);
>   	phys_addr_t mask = align - 1;
>   	unsigned long node = rmem->fdt_node;
> +	bool default_cma = of_get_flat_dt_prop(node, "linux,cma-default", NULL);
>   	struct cma *cma;
>   	int err;
>   
> +	if (size_cmdline != -1 && default_cma) {
> +		pr_info("Reserved memory: bypass %s node, using cmdline CMA params instead\n",
> +			rmem->name);
> +		return -EBUSY;
> +	}
> +
>   	if (!of_get_flat_dt_prop(node, "reusable", NULL) ||
>   	    of_get_flat_dt_prop(node, "no-map", NULL))
>   		return -EINVAL;
> @@ -322,7 +329,7 @@ static int __init rmem_cma_setup(struct reserved_mem *rmem)
>   	/* Architecture specific contiguous memory fixup. */
>   	dma_contiguous_early_fixup(rmem->base, rmem->size);
>   
> -	if (of_get_flat_dt_prop(node, "linux,cma-default", NULL))
> +	if (default_cma)
>   		dma_contiguous_set_default(cma);
>   
>   	rmem->ops = &rmem_cma_ops;
> 

For what it's worth,

Reviewed-by: Phil Elwell <phil@raspberrypi.org>

Phil