Re: [PATCH 2/2] spi: Add Analog Devices AXI SPI Engine controller support

Hi,

Thanks for review.

On 02/05/2016 03:04 PM, Andy Shevchenko wrote:
[...]

quoted

+++ b/drivers/spi/spi-axi-spi-engine.c

@@ -0,0 +1,591 @@

quoted

+static unsigned int spi_engine_get_clk_div(struct spi_engine *spi_engine,
+       struct spi_device *spi, struct spi_transfer *xfer)
+{
+       unsigned int clk_div;
+
+       clk_div = DIV_ROUND_UP(clk_get_rate(spi_engine->ref_clk),
+               xfer->speed_hz * 2);

quoted

+       if (clk_div > 255)
+               clk_div = 255;
+       else if (clk_div > 0)
+               clk_div -= 1;

255 is okay, 254 is not, 253- is okay. Why 254 is so special?

I don't see that. The condition is > 255, so everything greater or equal
than 256 gets mapped to 255. Everything else to x - 1, so 255 to 254, 254 to
253.

quoted

+
+       return clk_div;
+}

quoted

+static int spi_engine_compile_message(struct spi_engine *spi_engine,
+       struct spi_message *msg, bool dry, struct spi_engine_program *p)
+{
+       struct spi_device *spi = msg->spi;
+       struct spi_transfer *xfer;
+       int clk_div, new_clk_div;
+       bool cs_change = true;
+
+       clk_div = -1;
+
+       spi_engine_program_add_cmd(p, dry,
+               SPI_ENGINE_CMD_WRITE(SPI_ENGINE_CMD_REG_CONFIG,
+                       spi_engine_get_config(spi)));
+
+       list_for_each_entry(xfer, &msg->transfers, transfer_list) {
+               new_clk_div = spi_engine_get_clk_div(spi_engine, spi, xfer);

quoted

+               if (new_clk_div != clk_div) {
+                       clk_div = new_clk_div;
+                       spi_engine_program_add_cmd(p, dry,
+                               SPI_ENGINE_CMD_WRITE(SPI_ENGINE_CMD_REG_CLK_DIV,
+                                       clk_div));
+               }

Shouldn't be speed programmed per transfer?

Speed is programmed if it is not the same as the previous transfer. For the
first transfer in the message it always gets programmed.

quoted

+
+               if (cs_change)
+                       spi_engine_gen_cs(p, dry, spi, true);
+
+               spi_engine_gen_xfer(p, dry, xfer);
+               spi_engine_gen_sleep(p, dry, spi_engine, clk_div,
+                       xfer->delay_usecs);
+
+               cs_change = xfer->cs_change;
+               if (list_is_last(&xfer->transfer_list, &msg->transfers))
+                       cs_change = !cs_change;
+
+               if (cs_change)
+                       spi_engine_gen_cs(p, dry, spi, false);
+       }
+
+       return 0;
+}

[...]

quoted

+static bool spi_engine_write_tx_fifo(struct spi_engine *spi_engine)
+{
+       void __iomem *addr = spi_engine->base + SPI_ENGINE_REG_SDO_DATA_FIFO;
+       unsigned int n, m, i;
+       const uint8_t *buf;
+
+       n = readl_relaxed(spi_engine->base + SPI_ENGINE_REG_SDO_FIFO_ROOM);
+       while (n && spi_engine->tx_length) {
+               m = min(n, spi_engine->tx_length);
+               buf = spi_engine->tx_buf;

quoted

+               for (i = 0; i < m; i++)
+                       writel_relaxed(buf[i], addr);

writesl() ?

Hm, maybe. Does it really have the same semantics?

quoted

+               spi_engine->tx_buf += m;
+               spi_engine->tx_length -= m;
+               n -= m;
+               if (spi_engine->tx_length == 0)
+                       spi_engine_tx_next(spi_engine);
+       }
+
+       return spi_engine->tx_length != 0;
+}
+

[...]

quoted

+static int spi_engine_transfer_one_message(struct spi_master *master,
+       struct spi_message *msg)

And you are not using transfer_one() because of..?

transfer_one() does flow control in software. Execution is passed back to
software after each transfer and it also takes care of handling the chip
select assertion/deassertion as well as the delays. It's useful for hardware
which does not support hardware flow control. In this case the hardware
supports flow control including chip-select logic as well as delays. Making
use of this generates far less context switches per message and also has
predictable timings between transfers within a message.

[...]
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