Re: [PATCH 05/12] riscv: Implement non-coherent DMA support via SiFive cache flushing

[Ben Dooks <ben.dooks@xxxxxxxxxxxxxxx>]

On 11/02/2023 03:18, Cristian Ciocaltea wrote:
> From: Emil Renner Berthing <kernel@xxxxxxxx>
>
> This variant is used on the StarFive JH7100 SoC.
>
> Signed-off-by: Emil Renner Berthing <kernel@xxxxxxxx>
> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@xxxxxxxxxxxxx>
> ---
>   arch/riscv/Kconfig              |  6 ++++--
>   arch/riscv/mm/dma-noncoherent.c | 37 +++++++++++++++++++++++++++++++--
>   2 files changed, 39 insertions(+), 4 deletions(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 9c687da7756d..05f6c77faf6f 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -232,12 +232,14 @@ config LOCKDEP_SUPPORT
>   	def_bool y
>   
>   config RISCV_DMA_NONCOHERENT
> -	bool
> +	bool "Support non-coherent DMA"
> +	default SOC_STARFIVE
>   	select ARCH_HAS_DMA_PREP_COHERENT
> +	select ARCH_HAS_DMA_SET_UNCACHED
> +	select ARCH_HAS_DMA_CLEAR_UNCACHED
>   	select ARCH_HAS_SYNC_DMA_FOR_DEVICE
>   	select ARCH_HAS_SYNC_DMA_FOR_CPU
>   	select ARCH_HAS_SETUP_DMA_OPS
> -	select DMA_DIRECT_REMAP
>   
>   config AS_HAS_INSN
>   	def_bool $(as-instr,.insn r 51$(comma) 0$(comma) 0$(comma) t0$(comma) t0$(comma) zero)
> diff --git a/arch/riscv/mm/dma-noncoherent.c b/arch/riscv/mm/dma-noncoherent.c
> index d919efab6eba..e07e53aea537 100644
> --- a/arch/riscv/mm/dma-noncoherent.c
> +++ b/arch/riscv/mm/dma-noncoherent.c
> @@ -9,14 +9,21 @@
>   #include <linux/dma-map-ops.h>
>   #include <linux/mm.h>
>   #include <asm/cacheflush.h>
> +#include <soc/sifive/sifive_ccache.h>
>   
>   static bool noncoherent_supported;
>   
>   void arch_sync_dma_for_device(phys_addr_t paddr, size_t size,
>   			      enum dma_data_direction dir)
>   {
> -	void *vaddr = phys_to_virt(paddr);
> +	void *vaddr;
>   
> +	if (sifive_ccache_handle_noncoherent()) {
> +		sifive_ccache_flush_range(paddr, size);
> +		return;
> +	}
> +
> +	vaddr = phys_to_virt(paddr);
>   	switch (dir) {
>   	case DMA_TO_DEVICE:
>   		ALT_CMO_OP(clean, vaddr, size, riscv_cbom_block_size);
> @@ -35,8 +42,14 @@ void arch_sync_dma_for_device(phys_addr_t paddr, size_t size,
>   void arch_sync_dma_for_cpu(phys_addr_t paddr, size_t size,
>   			   enum dma_data_direction dir)
>   {
> -	void *vaddr = phys_to_virt(paddr);
> +	void *vaddr;
> +
> +	if (sifive_ccache_handle_noncoherent()) {
> +		sifive_ccache_flush_range(paddr, size);
> +		return;
> +	}

ok, what happens if we have an system where the ccache and another level
of cache also requires maintenance operations?

>   
> +	vaddr = phys_to_virt(paddr);
>   	switch (dir) {
>   	case DMA_TO_DEVICE:
>   		break;
> @@ -49,10 +62,30 @@ void arch_sync_dma_for_cpu(phys_addr_t paddr, size_t size,
>   	}
>   }
>   
> +void *arch_dma_set_uncached(void *addr, size_t size)
> +{
> +	if (sifive_ccache_handle_noncoherent())
> +		return sifive_ccache_set_uncached(addr, size);
> +
> +	return addr;
> +}
> +
> +void arch_dma_clear_uncached(void *addr, size_t size)
> +{
> +	if (sifive_ccache_handle_noncoherent())
> +		sifive_ccache_clear_uncached(addr, size);
> +}
> +
>   void arch_dma_prep_coherent(struct page *page, size_t size)
>   {
>   	void *flush_addr = page_address(page);
>   
> +	if (sifive_ccache_handle_noncoherent()) {
> +		memset(flush_addr, 0, size);
> +		sifive_ccache_flush_range(__pa(flush_addr), size);
> +		return;
> +	}
> +
>   	ALT_CMO_OP(flush, flush_addr, size, riscv_cbom_block_size);
>   }
>   

--
Ben Dooks				http://www.codethink.co.uk/
Senior Engineer				Codethink - Providing Genius

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