linux-kernel - Re: [PATCH v3 4/4] misc: fastrpc: Update dma

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Message-ID: <3gld6djjzfwu6rj47tz6gdwdpmh3hjexce5y6crqjus7ourgxf@puxrcpvijitl>
Date: Fri, 14 Nov 2025 10:00:25 -0600
From: Bjorn Andersson <andersson@...nel.org>
To: Kumari Pallavi <kumari.pallavi@....qualcomm.com>
Cc: kpallavi@....qualcomm.com, srini@...nel.org, amahesh@....qualcomm.com, 
	arnd@...db.de, gregkh@...uxfoundation.org, quic_bkumar@...cinc.com, 
	ekansh.gupta@....qualcomm.com, linux-kernel@...r.kernel.org, quic_chennak@...cinc.com, 
	dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org, jingyi.wang@....qualcomm.com, 
	aiqun.yu@....qualcomm.com, ktadakam@....qualcomm.com
Subject: Re: [PATCH v3 4/4] misc: fastrpc: Update dma_bits for CDSP support
 on Kaanapali SoC

On Fri, Nov 14, 2025 at 02:11:42PM +0530, Kumari Pallavi wrote:
> DSP currently supports 32-bit IOVA (32-bit PA + 4-bit SID) for
> both Q6 and user DMA (uDMA) access. This is being upgraded to
> 34-bit PA + 4-bit SID due to a hardware revision in CDSP for
> Kaanapali SoC, which expands the DMA addressable range.
> Update DMA bits configuration in the driver to support CDSP on
> Kaanapali SoC. Set the default `dma_bits` to 32-bit and update
> it to 34-bit based on CDSP and OF matching on the fastrpc node.
> 
> Signed-off-by: Kumari Pallavi <kumari.pallavi@....qualcomm.com>
> ---
>  drivers/misc/fastrpc.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> index bcf3c7f8d3e9..2eb8d37cd9b4 100644
> --- a/drivers/misc/fastrpc.c
> +++ b/drivers/misc/fastrpc.c
> @@ -267,6 +267,8 @@ struct fastrpc_session_ctx {
>  
>  struct fastrpc_soc_data {
>  	u32 sid_pos;
> +	u32 cdsp_dma_bits;
> +	u32 dsp_default_dma_bits;
>  };
>  
>  struct fastrpc_channel_ctx {
> @@ -2186,6 +2188,7 @@ static int fastrpc_cb_probe(struct platform_device *pdev)
>  	int i, sessions = 0;
>  	unsigned long flags;
>  	int rc;
> +	u32 dma_bits;
>  
>  	cctx = dev_get_drvdata(dev->parent);
>  	if (!cctx)
> @@ -2199,12 +2202,16 @@ static int fastrpc_cb_probe(struct platform_device *pdev)
>  		spin_unlock_irqrestore(&cctx->lock, flags);
>  		return -ENOSPC;
>  	}
> +	dma_bits = cctx->soc_data->dsp_default_dma_bits;
>  	sess = &cctx->session[cctx->sesscount++];
>  	sess->used = false;
>  	sess->valid = true;
>  	sess->dev = dev;
>  	dev_set_drvdata(dev, sess);
>  
> +	if (cctx->domain_id == CDSP_DOMAIN_ID)
> +		dma_bits = cctx->soc_data->cdsp_dma_bits;
> +
>  	if (of_property_read_u32(dev->of_node, "reg", &sess->sid))
>  		dev_info(dev, "FastRPC Session ID not specified in DT\n");
>  
> @@ -2219,9 +2226,9 @@ static int fastrpc_cb_probe(struct platform_device *pdev)
>  		}
>  	}
>  	spin_unlock_irqrestore(&cctx->lock, flags);
> -	rc = dma_set_mask(dev, DMA_BIT_MASK(32));
> +	rc = dma_set_mask(dev, DMA_BIT_MASK(dma_bits));
>  	if (rc) {
> -		dev_err(dev, "32-bit DMA enable failed\n");
> +		dev_err(dev, "%u-bit DMA enable failed\n", dma_bits);
>  		return rc;
>  	}
>  
> @@ -2308,10 +2315,14 @@ static int fastrpc_get_domain_id(const char *domain)
>  
>  static const struct fastrpc_soc_data kaanapali_soc_data = {
>  	.sid_pos = 56,
> +	.cdsp_dma_bits = 34,
> +	.dsp_default_dma_bits = 32,
>  };
>  
>  static const struct fastrpc_soc_data default_soc_data = {
>  	.sid_pos = 32,
> +	.cdsp_dma_bits = 32,
> +	.dsp_default_dma_bits = 32,

So, "dsp_default_dma_bits" specified "what is the dma_mask for the
non-CDSP fastrpc instances"? I don't find "dsp_default" to naturally
mean "not the cdsp".


Wouldn't it be better to introduce two different compatibles, one being
the "qcom,kaanapali-fastrpc" and one being the
"qcom,kaanapali-cdsp-fastrpc" and then use that to select things here?


PS. You store "dma_bits" just for the sake of turning it into a
dma_mask, just store the DMA_BIT_MASK() directly here instead.

Regards,
Bjorn

>  };
>  
>  static int fastrpc_rpmsg_probe(struct rpmsg_device *rpdev)
> -- 
> 2.34.1
> 
>