On 7/2/2026 11:05 AM, Ekansh Gupta wrote:
> On 09-06-2026 16:03, Vinayak Katoch wrote:
>> For ADSP, only a limited number of FastRPC context banks (CBs) are
>> available. Each CB supports a single session, which means only a few
>> processes can run on ADSP simultaneously. If all sessions are consumed
>> by fastrpc daemons, no session remains available when a user application
>> starts, causing the application to fail.
>>
>> To address this limitation, a Device Tree change was used till now:
>> qcom,nsessions = <5>;
>>
>> However, feedback from the upstream community indicated that this change
>> should not be made in the Device Tree. Instead, it was recommended to
>> handle this as a driver-level change.
>>
>> Instead of duplicating sessions inline during fastrpc_cb_probe() using
>> the qcom,nsessions DT property, defer duplication until after
>> of_platform_populate() returns in fastrpc_rpmsg_probe(), at which point
>> all compute-CB child nodes have been probed and the session array is
>> fully populated.
>>
>> For the ADSP domain, append FASTRPC_DUP_SESSIONS (4) copies of the
>> last probed session once of_platform_populate() succeeds. This keeps
>> the per-CB probe path simple and ensures duplicates are always derived
>> from a stable, fully-initialised session state.
>>
>> The qcom,nsessions DT property is no longer consumed by the driver; the
>> binding and DT sources are left unchanged.
>>
>> Signed-off-by: Vinayak Katoch <[email protected]>
>> ---
>> drivers/misc/fastrpc.c | 31 ++++++++++++++++++-------------
>> 1 file changed, 18 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
>> index 1080f9acf70a..46afbae9c234 100644
>> --- a/drivers/misc/fastrpc.c
>> +++ b/drivers/misc/fastrpc.c
>> @@ -30,6 +30,7 @@
>> #define CDSP_DOMAIN_ID (3)
>> #define GDSP_DOMAIN_ID (4)
>> #define FASTRPC_MAX_SESSIONS 14
>> +#define FASTRPC_DUP_SESSIONS 4
>> #define FASTRPC_MAX_VMIDS 16
>> #define FASTRPC_ALIGN 128
>> #define FASTRPC_MAX_FDLIST 16
>> @@ -2195,7 +2196,6 @@ static int fastrpc_cb_probe(struct platform_device
>> *pdev)
>> struct fastrpc_channel_ctx *cctx;
>> struct fastrpc_session_ctx *sess;
>> struct device *dev = &pdev->dev;
>> - int i, sessions = 0;
>> unsigned long flags;
>> int rc;
>> u32 dma_bits;
>> @@ -2204,8 +2204,6 @@ static int fastrpc_cb_probe(struct platform_device
>> *pdev)
>> if (!cctx)
>> return -EINVAL;
>>
>> - of_property_read_u32(dev->of_node, "qcom,nsessions", &sessions);
>> -
>> spin_lock_irqsave(&cctx->lock, flags);
>> if (cctx->sesscount >= FASTRPC_MAX_SESSIONS) {
>> dev_err(&pdev->dev, "too many sessions\n");
>> @@ -2225,16 +2223,6 @@ static int fastrpc_cb_probe(struct platform_device
>> *pdev)
>> if (of_property_read_u32(dev->of_node, "reg", &sess->sid))
>> dev_info(dev, "FastRPC Session ID not specified in DT\n");
>>
>> - if (sessions > 0) {
>> - struct fastrpc_session_ctx *dup_sess;
>> -
>> - for (i = 1; i < sessions; i++) {
>> - if (cctx->sesscount >= FASTRPC_MAX_SESSIONS)
>> - break;
>> - dup_sess = &cctx->session[cctx->sesscount++];
>> - memcpy(dup_sess, sess, sizeof(*dup_sess));
>> - }
>> - }
>> spin_unlock_irqrestore(&cctx->lock, flags);
>> rc = dma_set_mask(dev, DMA_BIT_MASK(dma_bits));
>> if (rc) {
>> @@ -2445,6 +2433,23 @@ static int fastrpc_rpmsg_probe(struct rpmsg_device
>> *rpdev)
>> if (err)
>> goto err_deregister_fdev;
>>
>> + if (data->domain_id == ADSP_DOMAIN_ID && data->sesscount > 0) {
>> + struct fastrpc_session_ctx *last_sess;
>> + struct fastrpc_session_ctx *dup_sess;
>> + unsigned long flags;
>> + int i;
> int i was already declared outside, avoid shadowing> +
Ack, will update in v2.>> + spin_lock_irqsave(&data->lock, flags);
>> + last_sess = &data->session[data->sesscount - 1];
>> + for (i = 0; i < FASTRPC_DUP_SESSIONS; i++) {
>> + if (data->sesscount >= FASTRPC_MAX_SESSIONS)
>> + break;
>> + dup_sess = &data->session[data->sesscount++];
>> + memcpy(dup_sess, last_sess, sizeof(*dup_sess));
>> + }
>> + spin_unlock_irqrestore(&data->lock, flags);
>> + }
>> +
>> return 0;
>>
>> err_deregister_fdev:
>>
>> ---
>> base-commit: 97e797263a5e963da3d1e66e743fd518567dfe37
>> change-id: 20260609-dup-sessions-ea2acaac1994
>>
>> Best regards,
>
