RE: [PATCH v4 2/4] drivers: dma: sh: Add DMAC driver for RZ/G2L SoC

Hi Vinod,

Thanks for the feedback.

Subject: Re: [PATCH v4 2/4] drivers: dma: sh: Add DMAC driver for RZ/G2L
SoC

On 19-07-21, 10:25, Biju Das wrote:

quoted

+struct rz_dmac_chan {
+	struct virt_dma_chan vc;
+	void __iomem *ch_base;
+	void __iomem *ch_cmn_base;
+	unsigned int index;
+	int irq;
+	struct rz_dmac_desc *desc;
+	int descs_allocated;
+
+	enum dma_slave_buswidth src_word_size;
+	enum dma_slave_buswidth dst_word_size;
+	dma_addr_t src_per_address;
+	dma_addr_t dst_per_address;
+
+	u32 chcfg;
+	u32 chctrl;
+	int mid_rid;
+
+	struct list_head ld_free;
+	struct list_head ld_queue;
+	struct list_head ld_active;
+
+	struct {
+		struct rz_lmdesc *base;
+		struct rz_lmdesc *head;
+		struct rz_lmdesc *tail;
+		int valid;
+		dma_addr_t base_dma;
+	} lmdesc;

should this be not part of rz_dmac_desc than channel?

No. It is channel specific. A channel has 64 HW legacy descriptors(see rz_dmac_chan_probe function) and 16 rz_dmac_desc( see rz_dmac_chan_resources function)

quoted

+static int rz_dmac_config(struct dma_chan *chan,
+			  struct dma_slave_config *config) {
+	struct rz_dmac_chan *channel = to_rz_dmac_chan(chan);
+	u32 *ch_cfg;
+
+	channel->src_per_address = config->src_addr;
+	channel->src_word_size = config->src_addr_width;
+	channel->dst_per_address = config->dst_addr;
+	channel->dst_word_size = config->dst_addr_width;
+
+	if (config->peripheral_config) {
+		ch_cfg = config->peripheral_config;
+		channel->chcfg = *ch_cfg;
+	}

can you explain what this the ch_cfg here and what does it represent?

It is a 32 bit value represent channel config value which supplied by each client driver during slave config.
It contains information like transfer mode,src/destination data size, Ack mode, Level type, DMA request on rising edge or falling
Edge, request direction etc...

For eg:- The channel config for SSI tx is (0x11228).
An example usage can be found here [1]

[1] https://patchwork.kernel.org/project/linux-renesas-soc/patch/20210719134040.7964-8-biju.das.jz@bp.renesas.com/

Regards,
Biju

--
~Vinod