linux-kernel - Re: [PATCH v2 1/3] misc: fastrpc: Rename phys to dma

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Message-ID: <75f6bbad-49a0-4a15-b976-a0450f66a4dc@oss.qualcomm.com>
Date: Thu, 23 Oct 2025 12:50:13 +0530
From: Kumari Pallavi <kumari.pallavi@....qualcomm.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....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 v2 1/3] misc: fastrpc: Rename phys to dma_addr for clarity



On 10/15/2025 3:37 PM, Dmitry Baryshkov wrote:
> On Wed, Oct 15, 2025 at 10:27:00AM +0530, Kumari Pallavi wrote:
>> Update all references of buf->phys and map->phys to buf->dma_addr and
>> map->dma_addr to accurately represent that these fields store DMA
>> addresses, not physical addresses. This change improves code clarity
>> and aligns with kernel conventions for dma_addr_t usage.
>>
>> Signed-off-by: Kumari Pallavi <kumari.pallavi@....qualcomm.com>
>> ---
>>   drivers/misc/fastrpc.c | 68 +++++++++++++++++++++---------------------
>>   1 file changed, 34 insertions(+), 34 deletions(-)
>>
>> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
>> index 621bce7e101c..975be54a2491 100644
>> --- a/drivers/misc/fastrpc.c
>> +++ b/drivers/misc/fastrpc.c
>> @@ -194,7 +194,7 @@ struct fastrpc_buf {
>>   	struct dma_buf *dmabuf;
>>   	struct device *dev;
>>   	void *virt;
>> -	u64 phys;
>> +	u64 dma_addr;
> 
> If it is dma_addr, why isn't it dma_addr_t?
> 

While the field is named dma_addr, it is not strictly limited to holding 
a DMA address.
Based on historical behavior, when the FASTRPC_ATTR_SECUREMAP flag is 
set, S2 mapping expects a physical address to be passed to the 
qcom_scm_assign_mem() API.
reference- 
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/drivers/misc/fastrpc.c?id=e90d911906196bf987492c94e38f10ca611dfd7b

> 
>>   	u64 size;
>>   	/* Lock for dma buf attachments */
>>   	struct mutex lock;
>> @@ -217,7 +217,7 @@ struct fastrpc_map {
>>   	struct dma_buf *buf;
>>   	struct sg_table *table;
>>   	struct dma_buf_attachment *attach;
>> -	u64 phys;
>> +	u64 dma_addr;
> 
> And this one.
> 
>>   	u64 size;
>>   	void *va;
>>   	u64 len;
>> @@ -406,12 +406,12 @@ static int __fastrpc_buf_alloc(struct fastrpc_user *fl, struct device *dev,
>>   
>>   	buf->fl = fl;
>>   	buf->virt = NULL;
>> -	buf->phys = 0;
>> +	buf->dma_addr = 0;
>>   	buf->size = size;
>>   	buf->dev = dev;
>>   	buf->raddr = 0;
>>   
>> -	buf->virt = dma_alloc_coherent(dev, buf->size, (dma_addr_t *)&buf->phys,
>> +	buf->virt = dma_alloc_coherent(dev, buf->size, (dma_addr_t *)&buf->dma_addr,
>>   				       GFP_KERNEL);
> 
> If it was dma_addr_t, you wouldn't have had to typecast here.
> 
>>   	if (!buf->virt) {
>>   		mutex_destroy(&buf->lock);
>> @@ -437,7 +437,7 @@ static int fastrpc_buf_alloc(struct fastrpc_user *fl, struct device *dev,
>>   	buf = *obuf;
>>   
>>   	if (fl->sctx && fl->sctx->sid)
>> -		buf->phys += ((u64)fl->sctx->sid << 32);
>> +		buf->dma_addr += ((u64)fl->sctx->sid << 32);
>>   
>>   	return 0;
>>   }
>> @@ -682,7 +682,7 @@ static int fastrpc_dma_buf_attach(struct dma_buf *dmabuf,
>>   		return -ENOMEM;
>>   
>>   	ret = dma_get_sgtable(buffer->dev, &a->sgt, buffer->virt,
>> -			      FASTRPC_PHYS(buffer->phys), buffer->size);
>> +			      FASTRPC_PHYS(buffer->dma_addr), buffer->size);
> 
> FASTRPC_PHYS trunates addr to 32 bits. Is it expected? Is it a DMA
> address on the  Linux or on the DSP side?
> 

Yes, it is expected as the device can address up to 32 bit memory range. 
It is a DMA address on the Linux.

>>   	if (ret < 0) {
>>   		dev_err(buffer->dev, "failed to get scatterlist from DMA API\n");
>>   		kfree(a);
> 

Thanks,
Pallavi