From f54701da5c0562cefadc8b638c3c141111c10579 Mon Sep 17 00:00:00 2001 From: Koichiro Den Date: Sun, 13 Sep 2026 02:40:21 +0900 Subject: [PATCH] dmaengine: Allow drivers to assign static channel IDs The dmaengine core assigns channel IDs in registration order. If a driver skips a hardware channel, chan_id can differ from the hardware numbering and a client cannot reliably correlate a requested channel with hardware resources. Let a driver request an exact channel ID before device registration. Reserve static IDs through the existing IDA so they remain unique, while retaining automatic IDA allocation as the default. For example, idma32 uses chan_id to select DMA_CTL_CH() and DMA_XBAR_SEL(), so it relies on ascending registration order to match chan_id with the hardware channel number. Use direction-flattened IDs for dw-edma channels. Unlike the direction-local hardware channel number, these IDs are unique within the DMA device. Suggested-by: Frank Li Reviewed-by: Frank Li Signed-off-by: Koichiro Den Link: https://lore.kernel.org/r/lm7tadnxsyrypu4mypptlkx5qkytex4qxsijdr5ydud2n3anvf@yakjfjg5ng4u/ Link: https://lore.kernel.org/r/20260813063757.3131865-2-den@valinux.co.jp/ Link: https://lore.kernel.org/r/an4TXwT37vWYEzCn@SMW015318/ Link: https://patch.msgid.link/20260912174023.1227397-2-den@valinux.co.jp Signed-off-by: Vinod Koul --- drivers/dma/dmaengine.c | 13 ++++++++----- drivers/dma/dw-edma/dw-edma-core.c | 1 + include/linux/dmaengine.h | 20 ++++++++++++++++++++ 3 files changed, 29 insertions(+), 5 deletions(-) diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c index bb30a9aa54d3..c5fef57b5adf 100644 --- a/drivers/dma/dmaengine.c +++ b/drivers/dma/dmaengine.c @@ -1078,6 +1078,7 @@ static int __dma_async_device_channel_register(struct dma_device *device, struct dma_chan *chan, const char *name) { + unsigned int id; int rc; chan->local = alloc_percpu(typeof(*chan->local)); @@ -1089,11 +1090,13 @@ static int __dma_async_device_channel_register(struct dma_device *device, goto err_free_local; } - /* - * When the chan_id is a negative value, we are dynamically adding - * the channel. Otherwise we are static enumerating. - */ - chan->chan_id = ida_alloc(&device->chan_ida, GFP_KERNEL); + if (chan->chan_id & DMA_CHAN_ID_STATIC) { + id = chan->chan_id & ~DMA_CHAN_ID_STATIC; + chan->chan_id = ida_alloc_range(&device->chan_ida, id, id, + GFP_KERNEL); + } else { + chan->chan_id = ida_alloc(&device->chan_ida, GFP_KERNEL); + } if (chan->chan_id < 0) { pr_err("%s: unable to alloc ida for chan: %d\n", __func__, chan->chan_id); diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c index e2eba6d72b53..4ed35e452d17 100644 --- a/drivers/dma/dw-edma/dw-edma-core.c +++ b/drivers/dma/dw-edma/dw-edma-core.c @@ -1119,6 +1119,7 @@ static int dw_edma_channel_setup(struct dw_edma *dw, u32 wr_alloc, u32 rd_alloc) &dw->chip->dt_region_rd[chan->id]; vchan_init(&chan->vc, dma); + dmaengine_set_static_chan_id(&chan->vc.chan, i); dw_edma_core_ch_config(chan); } diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h index c3a49a33307c..0ada6fe66e80 100644 --- a/include/linux/dmaengine.h +++ b/include/linux/dmaengine.h @@ -377,6 +377,26 @@ struct dma_chan { void *private; }; +#define DMA_CHAN_ID_STATIC BIT(30) + +/** + * dmaengine_set_static_chan_id - request an exact DMA engine channel ID + * @chan: DMA channel + * @id: channel ID, unique within the DMA device + * + * Drivers may call this after initializing @chan and before registering its + * DMA device. The dmaengine core reserves @id from the device IDA instead of + * assigning the next available ID. + */ +static inline void dmaengine_set_static_chan_id(struct dma_chan *chan, + unsigned int id) +{ + if (WARN_ON_ONCE(id >= DMA_CHAN_ID_STATIC)) + return; + + chan->chan_id = DMA_CHAN_ID_STATIC | id; +} + /** * struct dma_chan_dev - relate sysfs device node to backing channel device * @chan: driver channel device