linux-kernel - Re: [PATCH 2/2] arm-nommu: Add use_reserved_mem() to check if device support reserved memory

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Date:   Tue, 9 Jun 2020 15:08:14 +0100
From:   Vladimir Murzin <vladimir.murzin@....com>
To:     dillon.minfei@...il.com, robh+dt@...nel.org,
        mcoquelin.stm32@...il.com, alexandre.torgue@...com,
        linux@...linux.org.uk, kstewart@...uxfoundation.org,
        allison@...utok.net, info@...ux.net, tglx@...utronix.de
Cc:     devicetree@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] arm-nommu: Add use_reserved_mem() to check if device
 support reserved memory

On 6/8/20 9:30 AM, dillon.minfei@...il.com wrote:
> From: dillon min <dillon.minfei@...il.com>
> 
> Currently, we use dma direct to request coherent memory for driver on armv7m
> platform if 'cacheid' is zero, but dma_direct_can_mmap() is return false,
> dma_direct_mmap() return -ENXIO for CONFIG_MMU undefined platform.
> 
> so we have to back to use 'arm_nommu_dma_ops', add use_reserved_mem() to check
> if device support global or device corherent memory. if yes, then call
> set_dma_ops()
> 
> Signed-off-by: dillon min <dillon.minfei@...il.com>
> ---
>  arch/arm/mm/dma-mapping-nommu.c | 28 +++++++++++++++++++++++++++-
>  1 file changed, 27 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/mm/dma-mapping-nommu.c b/arch/arm/mm/dma-mapping-nommu.c
> index 287ef898a55e..e1c213fec152 100644
> --- a/arch/arm/mm/dma-mapping-nommu.c
> +++ b/arch/arm/mm/dma-mapping-nommu.c
> @@ -14,6 +14,7 @@
>  #include <asm/cacheflush.h>
>  #include <asm/outercache.h>
>  #include <asm/cp15.h>
> +#include <linux/of.h>
>  
>  #include "dma.h"
>  
> @@ -188,6 +189,31 @@ const struct dma_map_ops arm_nommu_dma_ops = {
>  };
>  EXPORT_SYMBOL(arm_nommu_dma_ops);
>  
> +static bool use_reserved_mem(struct device *dev)
> +{
> +	struct device_node *np;
> +
> +	np = of_find_node_by_path("/reserved-memory/linux,dma");
> +
> +	if (np &&
> +		of_device_is_compatible(np, "shared-dma-pool") &&
> +		of_property_read_bool(np, "no-map") &&
> +		of_property_read_bool(np, "linux,dma-default")) {
> +		/* has global corherent mem support */
> +		of_node_put(np);
> +		return true;
> +	}
> +
> +	np = of_parse_phandle(dev->of_node, "memory-region", 0);
> +	if (np) {
> +		/* has dev corherent mem support */
> +		of_node_put(np);
> +		return true;
> +	}
> +
> +	return false;
> +}
> +
>  void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
>  			const struct iommu_ops *iommu, bool coherent)
>  {
> @@ -206,6 +232,6 @@ void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
>  		dev->archdata.dma_coherent = (get_cr() & CR_M) ? coherent : true;
>  	}
>  
> -	if (!dev->archdata.dma_coherent)
> +	if (!dev->archdata.dma_coherent || use_reserved_mem(dev))
>  		set_dma_ops(dev, &arm_nommu_dma_ops);
>  }
> 

Sorry I have to NAK this hack :(

Digging git history reveled 79964a1c2972 ("ARM: 8633/1: nommu: allow mmap when !CONFIG_MMU")
which make me wonder if diff below does the trick for you

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 8f4bbda..8623b9e 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -456,14 +456,14 @@ int dma_direct_mmap(struct device *dev, struct vm_area_struct *vma,
 #else /* CONFIG_MMU */
 bool dma_direct_can_mmap(struct device *dev)
 {
-	return false;
+	return true;
 }
 
 int dma_direct_mmap(struct device *dev, struct vm_area_struct *vma,
 		void *cpu_addr, dma_addr_t dma_addr, size_t size,
 		unsigned long attrs)
 {
-	return -ENXIO;
+	return vm_iomap_memory(vma, vma->vm_start, (vma->vm_end - vma->vm_start));;
 }
 #endif /* CONFIG_MMU */

Cheers
Vladimir