Hi Ira,
Ira Snyder wrote:
Use the DMA_SLAVE capability of the DMAEngine API to copy/from a
scatterlist into an arbitrary list of hardware address/length pairs.
This allows a single DMA transaction to copy data from several different
devices into a scatterlist at the same time.
This also adds support to enable some controller-specific features such as
external start and external pause of a DMA transaction.
Signed-off-by: Ira W. Snyder <i...@ovro.caltech.edu>
---
This is a request for comments on this patch. I hunch it is not quite
ready for inclusion, though it is certainly ready for review. Correct
functioning of this patch depends on the patches submitted earlier.
As suggested by Dan Williams, I implemented DMA_SLAVE support for the
fsldma controller to allow me to use the hardware to transfer to/from a
scatterlist to a list of hardware address/length pairs.
I implemented support for the extra features available in the DMA
controller, such as external pause and external start. I have not tested
the features yet. I am willing to drop the support if everything else
looks good.
I have implemented helper functions for creating the list of hardware
address/length pairs as static inline functions in the linux/fsldma.h
header. Should I incorporate these into the driver itself and use
EXPORT_SYMBOL()? I've never done this before :)
Using EXPORT_SYMBOL would defeat the purpose of conforming to the
dmaengine api which should allow other subsystems to generically
discover an fsldma resource.
diff --git a/include/linux/fsldma.h b/include/linux/fsldma.h
new file mode 100644
index 0000000..a42dcdd
--- /dev/null
+++ b/include/linux/fsldma.h
@@ -0,0 +1,105 @@
+/*
+ * Freescale MPC83XX / MPC85XX DMA Controller
+ *
+ * Copyright (c) 2009 Ira W. Snyder <i...@ovro.caltech.edu>
+ *
+ * This file is licensed under the terms of the GNU General Public License
+ * version 2. This program is licensed "as is" without any warranty of any
+ * kind, whether express or implied.
+ */
+
+#ifndef __LINUX_FSLDMA_H__
+#define __LINUX_FSLDMA_H__
+
+#include <linux/dmaengine.h>
+
+/*
+ * physical hardware address / length pair for use with the
+ * DMAEngine DMA_SLAVE API
+ */
+struct fsl_dma_hw_addr {
+ struct list_head entry;
+
+ dma_addr_t address;
+ size_t length;
+};
Can you explain a bit more why you need the new dma address list, would
a struct scatterlist suffice?
In general it is difficult to merge new functionality without an in-tree
user. Can you share the client of this new api?
I suspect you can get away without needing these new helper routines.
Have a look at how Haavard implemented his DMA_SLAVE client in
drivers/mmc/host/atmel-mci.c.
Haavard ended up needing to add some public structure definitions to
include/linux, but my preference is to keep this in an
architecture/platform specific header file location if possible.
Regards,
Dan
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