[PATCH V2 6/8] dmaengine: bcm2835: move controlblock chain generation into separate method

[Eric Anholt]

kernel at martin.sperl.org writes:

> From: Martin Sperl <kernel at martin.sperl.org>
>
> In preparation of adding slave_sg functionality this patch moves the
> generation/allocation of bcm2835_desc and the building of
> the corresponding DMA-control-block chain from bcm2835_dma_prep_dma_cyclic
> into the newly created method bcm2835_dma_create_cb_chain.
>
> This new code also takes the limits of LITE channels into account
> and splits the control-block transfers at the correct location.
>
> Tested Audio output with a Hifiberry I2S card.
>
> Signed-off-by: Martin Sperl <kernel at martin.sperl.org>
> ---
>  drivers/dma/bcm2835-dma.c |  288 ++++++++++++++++++++++++++++++---------------
>  1 file changed, 191 insertions(+), 97 deletions(-)
>
> diff --git a/drivers/dma/bcm2835-dma.c b/drivers/dma/bcm2835-dma.c
> index 43758ba..41a4f0b 100644
> --- a/drivers/dma/bcm2835-dma.c
> +++ b/drivers/dma/bcm2835-dma.c
> @@ -90,12 +90,12 @@ struct bcm2835_desc {
>  	struct virt_dma_desc vd;
>  	enum dma_transfer_direction dir;
>
> -	struct bcm2835_cb_entry *cb_list;
> -
>  	unsigned int frames;
>  	size_t size;
>
>  	bool cyclic;
> +
> +	struct bcm2835_cb_entry cb_list[];
>  };
>
>  #define BCM2835_DMA_CS		0x00
> @@ -181,6 +181,22 @@ struct bcm2835_desc {
>  #define BCM2835_DMA_IRQ_SHARED		11
>  #define BCM2835_DMA_IRQ_ALL		12
>
> +/* the max dma length for different channels */
> +#define MAX_DMA_LEN SZ_1G
> +#define MAX_LITE_DMA_LEN (SZ_64K - 4)
> +
> +static inline bool bcm2835_dma_is_lite(struct bcm2835_chan *c)
> +{
> +	/* dma channels >= 7 are LITE channels */
> +	return (c->ch >= 7);
> +}

You can ask a channel if it's a LITE engine by checking if the DEBUG reg
has bit 28 set.  Then you don't need to have the software/DT guessing
about it.

However, I'm disappointed to see these changes for adding LITE support
included in the same commit as refactoring chain generation into a
separate function.
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