[PATCH]: Fix DMAR Error NO_PASID when IOMMU is enabled

[Eric Debief <debief@xxxxxxxxxxxx>]

Hi,

We had a "DMAR Error  NO PASID" error reported in the kernel's log
when the IOMMU was enabled.

This is due to the missing WriteBack area for the C2H stream.
Below my patch.
One point : I didn't compile it within the latest kernel's sources'
tree as it is an extract of our backport of the XDMA support.
Feel free to contact me on any issue with this.

Hope this helps,
Eric.


================================================
>From 7db026854cd291677b08e8d137ef4238c8ea96db Mon Sep 17 00:00:00 2001
From: Eric DEBIEF <debief@xxxxxxxxxxxx>
Date: Mon, 29 Apr 2024 15:36:24 +0200
Subject: FIX: DMAR Error with IO_MMU.C2H write-back was not set and leads to
 DMAR Error with IOMMU. Add the Writeback structure, allocate it, set it as
 the Src field in the descriptor. Done for all preps functions.

---
 drivers/dma/xilinx/xdma.c | 41 +++++++++++++++++++++++++++++++++++----
 1 file changed, 37 insertions(+), 4 deletions(-)

diff --git a/drivers/dma/xilinx/xdma.c b/drivers/dma/xilinx/xdma.c
index 9c84211d26a1..306099c920bb 100644
--- a/drivers/dma/xilinx/xdma.c
+++ b/drivers/dma/xilinx/xdma.c
@@ -51,6 +51,20 @@ struct xdma_desc_block {
  dma_addr_t dma_addr;
 };

+/**
+ * struct xdma_c2h_write_back  - Write back block , written by the XDMA.
+ * @magic_status_bit : magic (0x52B4) once written
+ * @length: effective transfer length (in bytes)
+ * @PADDING to be aligned on 32 bytes
+ * @associated dma address
+ */
+struct xdma_c2h_write_back {
+ __le32 magic_status_bit;
+ __le32 length;
+ u32 padding_1[6];
+ dma_addr_t dma_addr;
+};
+
 /**
  * struct xdma_chan - Driver specific DMA channel structure
  * @vchan: Virtual channel
@@ -61,6 +75,8 @@ struct xdma_desc_block {
  * @dir: Transferring direction of the channel
  * @cfg: Transferring config of the channel
  * @irq: IRQ assigned to the channel
+ * @write_back : C2H meta data write back
+
  */
 struct xdma_chan {
  struct virt_dma_chan vchan;
@@ -73,6 +89,7 @@ struct xdma_chan {
  u32 irq;
  struct completion last_interrupt;
  bool stop_requested;
+ struct xdma_c2h_write_back* write_back;
 };

 /**
@@ -628,7 +645,7 @@ xdma_prep_device_sg(struct dma_chan *chan, struct
scatterlist *sgl,
  src = &addr;
  dst = &dev_addr;
  } else {
- dev_addr = xdma_chan->cfg.src_addr;
+ dev_addr = xdma_chan->cfg.src_addr ? xdma_chan->cfg.src_addr :
xdma_chan->write_back->dma_addr;
  src = &dev_addr;
  dst = &addr;
  }
@@ -705,7 +722,7 @@ xdma_prep_dma_cyclic(struct dma_chan *chan,
dma_addr_t address,
  src = &addr;
  dst = &dev_addr;
  } else {
- dev_addr = xdma_chan->cfg.src_addr;
+ dev_addr = xdma_chan->cfg.src_addr ? xdma_chan->cfg.src_addr :
xdma_chan->write_back->dma_addr;
  src = &dev_addr;
  dst = &addr;
  }
@@ -803,6 +820,9 @@ static void xdma_free_chan_resources(struct dma_chan *chan)
  struct xdma_chan *xdma_chan = to_xdma_chan(chan);

  vchan_free_chan_resources(&xdma_chan->vchan);
+ dma_pool_free(xdma_chan->desc_pool,
+ xdma_chan->write_back,
+   xdma_chan->write_back->dma_addr);
  dma_pool_destroy(xdma_chan->desc_pool);
  xdma_chan->desc_pool = NULL;
 }
@@ -816,6 +836,7 @@ static int xdma_alloc_chan_resources(struct dma_chan *chan)
  struct xdma_chan *xdma_chan = to_xdma_chan(chan);
  struct xdma_device *xdev = xdma_chan->xdev_hdl;
  struct device *dev = xdev->dma_dev.dev;
+ dma_addr_t write_back_addr;

  while (dev && !dev_is_pci(dev))
  dev = dev->parent;
@@ -824,13 +845,25 @@ static int xdma_alloc_chan_resources(struct
dma_chan *chan)
  return -EINVAL;
  }

- xdma_chan->desc_pool = dma_pool_create(dma_chan_name(chan), dev,
XDMA_DESC_BLOCK_SIZE,
-       XDMA_DESC_BLOCK_ALIGN, XDMA_DESC_BLOCK_BOUNDARY);
+ //Allocate the pool WITH the H2C write back
+ xdma_chan->desc_pool = dma_pool_create(dma_chan_name(chan),
+ dev,
+ XDMA_DESC_BLOCK_SIZE + sizeof(struct xdma_c2h_write_back),
+ XDMA_DESC_BLOCK_ALIGN,
+ XDMA_DESC_BLOCK_BOUNDARY);
  if (!xdma_chan->desc_pool) {
  xdma_err(xdev, "unable to allocate descriptor pool");
  return -ENOMEM;
  }

+ /* Allocate the C2H write back out of the pool*/
+ xdma_chan->write_back = dma_pool_alloc(xdma_chan->desc_pool,
GFP_NOWAIT, &write_back_addr);
+ if (!xdma_chan->write_back) {
+ xdma_err(xdev, "unable to allocate C2H write back block");
+ return -ENOMEM;
+ }
+ xdma_chan->write_back->dma_addr = write_back_addr;
+
  return 0;
 }

-- 
2.34.1

-- 
 
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