Re: [PATCH v4 2/3] dmaengine: add peripheral configuration

[Vinod Koul <vkoul@kernel.org>]

On 09-10-20, 13:45, Peter Ujfalusi wrote:
> Hi Vinod,
> 
> On 09/10/2020 13.30, Vinod Koul wrote:
> > Hi Peter,
> > 
> > On 09-10-20, 12:04, Peter Ujfalusi wrote:
> >> On 08/10/2020 15.31, Vinod Koul wrote:
> >>> Some complex dmaengine controllers have capability to program the
> >>> peripheral device, so pass on the peripheral configuration as part of
> >>> dma_slave_config
> >>>
> >>> Signed-off-by: Vinod Koul <vkoul@kernel.org>
> >>> ---
> >>>  include/linux/dmaengine.h | 5 +++++
> >>>  1 file changed, 5 insertions(+)
> >>>
> >>> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> >>> index 6fbd5c99e30c..a15dc2960f6d 100644
> >>> --- a/include/linux/dmaengine.h
> >>> +++ b/include/linux/dmaengine.h
> >>> @@ -418,6 +418,9 @@ enum dma_slave_buswidth {
> >>>   * @slave_id: Slave requester id. Only valid for slave channels. The dma
> >>>   * slave peripheral will have unique id as dma requester which need to be
> >>>   * pass as slave config.
> >>> + * @peripheral_config: peripheral configuration for programming peripheral
> >>> + * for dmaengine transfer
> >>> + * @peripheral_size: peripheral configuration buffer size
> >>>   *
> >>>   * This struct is passed in as configuration data to a DMA engine
> >>>   * in order to set up a certain channel for DMA transport at runtime.
> >>> @@ -443,6 +446,8 @@ struct dma_slave_config {
> >>>  	u32 dst_port_window_size;
> >>>  	bool device_fc;
> >>>  	unsigned int slave_id;
> >>> +	void *peripheral_config;
> >>> +	size_t peripheral_size;
> >>
> >> Do you foresee a need of src/dst pair of these?
> >> If we do DEV_TO_DEV with different type of peripherals it is going to
> >> cause issues.
> > 
> > Not really as the channel already has direction and this is per channel.
> 
> Yes, in case of DEV_TO_MEM or MEM_TO_DEV.
> 
> > If for any any reason subsequent txn is for different direction, I would
> > expect that parameters are set again before prep_ calls
> 
> But in DEV_TO_DEV?

Do we support that :D

> If we have two peripherals, both needs config:
> p1_config and p2_config
> 
> What and how would one use the single peripheral_config?

Since the config is implementation specific, I do not think it limits.
You may create

struct peter_config {
        struct p1_config;
        struct p2_config;
};

> 
> If only one of them needs config, then sure, the driver can pin-point
> which one the single config might apply to.
> 
> Or you chain the same type of peripheral and you would need different
> config for tx and rx?
> 
> - Péter
> 
> Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
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-- 
~Vinod