Hi Vinod,
On Sun, Jan 26, 2014 at 7:29 PM, Vinod Koul <vinod.koul@xxxxxxxxx> wrote:
> On Fri, Jan 24, 2014 at 02:24:27PM +0100, Lars-Peter Clausen wrote:
>> On 01/24/2014 12:16 PM, Srikanth Thokala wrote:
>> > Hi Lars,
>> >
>> > On Thu, Jan 23, 2014 at 4:55 PM, Lars-Peter Clausen <lars@xxxxxxxxxx> wrote:
>> >> On 01/22/2014 05:52 PM, Srikanth Thokala wrote:
>> >> [...]
>> >>> +/**
>> >>> + * xilinx_vdma_device_control - Configure DMA channel of the device
>> >>> + * @dchan: DMA Channel pointer
>> >>> + * @cmd: DMA control command
>> >>> + * @arg: Channel configuration
>> >>> + *
>> >>> + * Return: '0' on success and failure value on error
>> >>> + */
>> >>> +static int xilinx_vdma_device_control(struct dma_chan *dchan,
>> >>> + enum dma_ctrl_cmd cmd, unsigned long arg)
>> >>> +{
>> >>> + struct xilinx_vdma_chan *chan = to_xilinx_chan(dchan);
>> >>> +
>> >>> + switch (cmd) {
>> >>> + case DMA_TERMINATE_ALL:
>> >>> + xilinx_vdma_terminate_all(chan);
>> >>> + return 0;
>> >>> + case DMA_SLAVE_CONFIG:
>> >>> + return xilinx_vdma_slave_config(chan,
>> >>> + (struct xilinx_vdma_config *)arg);
>> >>
>> >> You really shouldn't be overloading the generic API with your own semantics.
>> >> DMA_SLAVE_CONFIG should take a dma_slave_config and nothing else.
>> >
>> > Ok. The driver needs few additional configuration from the slave
>> > device like Vertical
>> > Size, Horizontal Size, Stride etc., for the DMA transfers, in that case do you
>> > suggest me to define a separate dma_ctrl_cmd like the one FSLDMA_EXTERNAL_START
>> > defined for Freescale drivers?
>>
>> In my opinion it is not a good idea to have driver implement a generic API,
>> but at the same time let the driver have custom semantics for those API
>> calls. It's a bit like having a gpio driver that expects 23 and 42 as the
>> values passed to gpio_set_value instead of 0 and 1. It completely defeats
>> the purpose of a generic API, namely that you are able to write generic code
>> that makes use of the API without having to know about which implementation
>> API it is talking to. The dmaengine framework provides the
>> dmaengine_prep_interleaved_dma() function to setup two dimensional
>> transfers, e.g. take a look at sirf-dma.c or imx-dma.c.
>
> The question here i think would be waht this device supports? Is the hardware
> capable of doing interleaved transfers, then would make sense.
>
> While we do try to get users use dma_slave_config, but there will always be
> someone who have specfic params. If we can generalize then we might want to add
> to the dma_slave_config as well
There are many configuration parameters which are specific to IP and I
would like to
give an overview of some of parameteres here:
1) Park Mode ('cfg->park'): In Park mode, engine will park on frame
referenced by
'cfg->park_frm', so user will have control on each frame in this mode.
2) Interrupt Coalesce ('cfg->coalesce'): Used for setting interrupt
threshold. This value
determines the number of frame buffers to process. To use this feature,
'cfg->frm_cnt_en' should be set.
3) Frame Synchronization Source ('cfg->ext_fsync'): Can be an
external/internal frame
synchronization source. Used to synchronize one channel (MM2S/S2MM) with
another (S2MM/MM2S) channel.
4) Genlock Synchronization ('cfg->genlock'): Used to avoid mismatch rate between
master and slave. In master mode (cfg->master), frames are not dropped and
slave can drop frames to adjust to master frame rate.
And in future, this Engine being a soft IP, we could expect some more additional
parameters. Isn't a good idea to have a private member in dma_slave_config for
sharing additional configuration between slave device and dma engine? Or a new
dma_ctrl_cmd like FSLDMA_EXTERNAL_START?
Srikanth
>
> --
> ~Vinod
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