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

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On 2/13/23 10:30, Ben Dooks wrote:
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?

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);
  }




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