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

[Cristian Ciocaltea]

On 2/13/23 10:30, Ben Dooks wrote:
> On 11/02/2023 03:18, Cristian Ciocaltea wrote:
>> From: Emil Renner Berthing <kernel at esmil.dk>
>>
>> This variant is used on the StarFive JH7100 SoC.
>>
>> Signed-off-by: Emil Renner Berthing <kernel at esmil.dk>
>> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea at collabora.com>
>> ---
>>   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?

According to [1], the handling of non-coherent DMA on RISC-V is 
currently being worked on, so I will respin the series as soon as the 
proper support arrives.

[1] https://lore.kernel.org/lkml/Y+d36nz0xdfXmDI1@spud/


>> +    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);
>>   }
>