Re: [PATCH v3 2/2] dmaengine: apple-admac: Add M3 generation ADMACs

On Wed, Aug 12, 2026 at 11:26:34AM +0200, Sasha Finkelstein wrote:
> The admacs present on t8122 and t603x SoCs need additional writes in
> order to operate correctly. The exact purpose of this register
> is unknown
>
> Signed-off-by: Sasha Finkelstein <[email protected]>
> ---
>  drivers/dma/apple-admac.c | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
>
> diff --git a/drivers/dma/apple-admac.c b/drivers/dma/apple-admac.c
> index 14a5ee14a481..fd6236c7c024 100644
> --- a/drivers/dma/apple-admac.c
> +++ b/drivers/dma/apple-admac.c
> @@ -39,10 +39,14 @@
>
>  #define FLAG_DESC_NOTIFY	BIT(16)
>
> +#define T8122_UNK_28_VAL	0x200000
> +
>  #define REG_TX_START		0x0000
>  #define REG_TX_STOP		0x0004
>  #define REG_RX_START		0x0008
>  #define REG_RX_STOP		0x000c
> +#define REG_UNK_28		0x0028
> +#define REG_UNK_2C		0x002c
>  #define REG_IMPRINT		0x0090
>  #define REG_TX_SRAM_SIZE	0x0094
>  #define REG_RX_SRAM_SIZE	0x0098
> @@ -127,6 +131,7 @@ struct admac_data {
>  	struct mutex cache_alloc_lock;
>  	struct admac_sram txcache, rxcache;
>
> +	bool set_unk28;

const struct admac_hw *drvdata;

So needn't copy set_unk28 to here, in case need more quirk in future

Frank

>  	int irq;
>  	int irq_index;
>  	int nchannels;
> @@ -147,6 +152,10 @@ struct admac_tx {
>  	struct list_head node;
>  };
>
> +struct admac_hw {
> +	bool set_unk28;
> +};
> +
>  static int admac_alloc_sram_carveout(struct admac_data *ad,
>  				     enum dma_transfer_direction dir,
>  				     u32 *out)
> @@ -747,6 +756,11 @@ static int admac_device_config(struct dma_chan *chan,
>  	u32 bus_width = readl_relaxed(ad->base + REG_BUS_WIDTH(adchan->no)) &
>  		~(BUS_WIDTH_WORD_SIZE | BUS_WIDTH_FRAME_SIZE);
>
> +	if (ad->set_unk28) {
> +		writel_relaxed(T8122_UNK_28_VAL, ad->base + REG_UNK_28);
> +		writel_relaxed(T8122_UNK_28_VAL, ad->base + REG_UNK_2C);
> +	}
> +
>  	switch (is_tx ? config->dst_addr_width : config->src_addr_width) {
>  	case DMA_SLAVE_BUSWIDTH_1_BYTE:
>  		wordsize = 1;
> @@ -805,6 +819,7 @@ static int admac_probe(struct platform_device *pdev)
>  	struct device_node *np = pdev->dev.of_node;
>  	struct admac_data *ad;
>  	struct dma_device *dma;
> +	const struct admac_hw *hw;
>  	int nchannels;
>  	int err, irq, i;
>
> @@ -822,6 +837,9 @@ static int admac_probe(struct platform_device *pdev)
>  	ad->dev = &pdev->dev;
>  	ad->nchannels = nchannels;
>  	mutex_init(&ad->cache_alloc_lock);
> +	hw = of_device_get_match_data(&pdev->dev);
> +	if (hw)
> +		ad->set_unk28 = hw->set_unk28;
>
>  	/*
>  	 * The controller has 4 IRQ outputs. Try them all until
> @@ -935,7 +953,12 @@ static void admac_remove(struct platform_device *pdev)
>  	reset_control_rearm(ad->rstc);
>  }
>
> +static const struct admac_hw admac_t8122_hw = {
> +	.set_unk28 = true,
> +};
> +
>  static const struct of_device_id admac_of_match[] = {
> +	{ .compatible = "apple,t8122-admac", .data = &admac_t8122_hw },
>  	{ .compatible = "apple,t8103-admac", },
>  	{ .compatible = "apple,admac", },
>  	{ }
>
> --
> 2.55.0
>