Re: [PATCH v2 04/14] dmaengine: Add metadata_ops for dma_async_tx_descriptor

On 08/09/2019 17.12, Vinod Koul wrote:

On 30-07-19, 12:34, Peter Ujfalusi wrote:

quoted

The metadata is best described as side band data or parameters traveling
alongside the data DMAd by the DMA engine. It is data
which is understood by the peripheral and the peripheral driver only, the
DMA engine see it only as data block and it is not interpreting it in any
way.

The metadata can be different per descriptor as it is a parameter for the
data being transferred.

If the DMA supports per descriptor metadata it can implement the attach,
get_ptr/set_len callbacks.

Client drivers must only use either attach or get_ptr/set_len to avoid
misconfiguration.

Client driver can check if a given metadata mode is supported by the
channel during probe time with
dmaengine_is_metadata_mode_supported(chan, DESC_METADATA_CLIENT);
dmaengine_is_metadata_mode_supported(chan, DESC_METADATA_ENGINE);

and based on this information can use either mode.

Wrappers are also added for the metadata_ops.

To be used in DESC_METADATA_CLIENT mode:
dmaengine_desc_attach_metadata()

To be used in DESC_METADATA_ENGINE mode:
dmaengine_desc_get_metadata_ptr()
dmaengine_desc_set_metadata_len()

Signed-off-by: Peter Ujfalusi <redacted>
---
 drivers/dma/dmaengine.c   |  73 ++++++++++++++++++++++++++
 include/linux/dmaengine.h | 108 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 181 insertions(+)

diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 03ac4b96117c..6baddf7dcbfd 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c

@@ -1302,6 +1302,79 @@ void dma_async_tx_descriptor_init(struct dma_async_tx_descriptor *tx,
 }
 EXPORT_SYMBOL(dma_async_tx_descriptor_init);
 
+static inline int desc_check_and_set_metadata_mode(
+	struct dma_async_tx_descriptor *desc, enum dma_desc_metadata_mode mode)
+{
+	/* Make sure that the metadata mode is not mixed */
+	if (!desc->desc_metadata_mode) {
+		if (dmaengine_is_metadata_mode_supported(desc->chan, mode))
+			desc->desc_metadata_mode = mode;

So do we have different descriptors supporting different modes or is it
controlled based? For latter we can do this check at controller
registration!

It is actually on channel basis (in UDMAP):
TR channel does not support metadata at all.
Packet Mode channel have support for metadata, but it might not be
available for certain remote peripherals. PDMAs for example does not use
metadata.
Any channel can be configured as TR or Packet Mode, any channel can
service a peripheral which needs or does not need metadata.

The reason we ended up per descriptor callbacks with Radhey (added to
CC) is that all functions operate on the descriptor and it was natural
to have them attached to the descriptor rather than add channel based
callbacks which must also take the descriptor pointer in addition. The
descriptor have pointer to the channel it is issued on.

I only know if metadata is going to be supported when the channel is
requested, based on the psil-config of the remote thread.

Clients still can check and plan ahead on how to use the metadata.

- Péter

Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki

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