Hi John,

On Thu, 26 Mar 2026 at 23:42, John Madieu [off-list ref] wrote:

quoted

From: Geert Uytterhoeven <geert@linux-m68k.org>
On Thu, 19 Mar 2026 at 16:55, John Madieu [off-list ref]
wrote:

quoted

Some peripherals on RZ/V2H, RZ/V2N, and RZ/G3E SoCs require explicit
ACK signal routing through the ICU. Document the optional second cell
in the DMA specifier for specifying the ACK signal number.

The first cell remains unchanged and specifies the encoded MID/RID and
channel configuration. The optional second cell specifies the DMA ACK
signal number for peripherals requiring level-based handshaking.

Signed-off-by: John Madieu <john.madieu.xa@bp.renesas.com>

Thanks for your patch!

Just a quick head-up, as I haven't read the actual secion in the
documentation yet.

quoted

--- a/Documentation/devicetree/bindings/dma/renesas,rz-dmac.yaml
+++ b/Documentation/devicetree/bindings/dma/renesas,rz-dmac.yaml

@@ -63,17 +63,27 @@ properties:
       - const: register

   '#dma-cells':
-    const: 1
-    description:
+    description: |
       The cell specifies the encoded MID/RID or the REQ No values of
       the DMAC port connected to the DMA client and the slave channel
       configuration parameters.
+      Use 1 cell for basic DMA configuration.
+      Use 2 cells when DMA ACK signal routing through ICU is required
+      (RZ/V2H, RZ/V2N, RZ/G3E audio peripherals such as SSIU, SPDIF,

SRC, DVC).

quoted

+
+      First cell:
       bits[0:9] - Specifies the MID/RID or the REQ No value
       bit[10] - Specifies DMA request high enable (HIEN)
       bit[11] - Specifies DMA request detection type (LVL)
       bits[12:14] - Specifies DMAACK output mode (AM)
       bit[15] - Specifies Transfer Mode (TM)

+      Second cell (optional, when #dma-cells = <2>):
+      bits[6:0] - DMA acknowledge signal number (from ICU ACK table),
+                  where 0 is a valid signal number.
+                  Required for peripherals using level-based DMA
+                  handshaking (SSIU, SPDIF, RSPI, SCU, ADC, PDM).

How do you expect this to work? #dma-cells applies to all DMA consumers of
this provider, and these SoCs already have DMA users relying on #dma-cells
being one.

Indeed.

quoted

In addition, you cannot have optional cells: if #dma-cells is two, then
all consumers must supply two cells (of course we could switch all of them
to two cells at once).  However, as zero is a valid signal number, we
cannot use that as a dummy when no DMA acknowledge signal number is needed
(we could use e.g. 0xffffffff instead).

Is there any other way to provide this information?
E.g. could we have a table in the driver that contains this info for the
(presumably few) MID/RID values that need it?

There are actually 89 entries, and I could identify 3 peripheral
group with linear ACK assignments. Thus instead of static array
we would get a simple function handling 3 req_no ranges.

Something like:

/*
 * Map MID/RID request number (bits[0:9] of DMA specifier) to the ICU
 * DMA ACK signal number, per RZ/G3E hardware manual Table 4.6-28.
 *
 * Three peripheral groups with linear ACK assignment:
 *
 *   PFC external DMA pins (DREQ0..DREQ4):
 *     req_no 0x000-0x004 -> ACK No. 84-88  (ack = req_no + 84)
 *
 *   SSIU BUSIFs (ssip00..ssip93):
 *     req_no 0x161-0x198 -> ACK No. 28-83  (ack = req_no - 0x145)
 *
 *   SPDIF (CH0..CH2) + SCU SRC (sr0..sr9) + DVC (cmd0..cmd1):
 *     req_no 0x199-0x1b4 -> ACK No. 0-27   (ack = req_no - 0x199)
 */
static int rz_dmac_get_ack_no(const struct rz_dmac_info *info, u16 req_no)
{
        if (!info->icu_register_dma_ack)
                return -EINVAL;

        /* PFC external DMA pins: ACK No. 84-88 */
        if (req_no <= 0x004)
                return req_no + 84;

        /* SSIU BUSIFs: ACK No. 28-83 */
        if (req_no >= 0x161 && req_no <= 0x198)
                return req_no - 0x145;

        /* SPDIF + SCU SRC + DVC: ACK No. 0-27 */
        if (req_no >= 0x199 && req_no <= 0x1b4)
                return req_no - 0x199;

        return -EINVAL;
}

Nice!

Note that you can use ranges in case statements:

    git grep "case.*\.\.\."

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds