linux-kernel - [PATCH v1 2/3] misc: fastrpc: Update context ID mask for polling mode support

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Message-Id: <20250901053336.3939595-3-ekansh.gupta@oss.qualcomm.com>
Date: Mon,  1 Sep 2025 11:03:35 +0530
From: Ekansh Gupta <ekansh.gupta@....qualcomm.com>
To: srini@...nel.org, linux-arm-msm@...r.kernel.org
Cc: gregkh@...uxfoundation.org, quic_bkumar@...cinc.com,
        linux-kernel@...r.kernel.org, quic_chennak@...cinc.com,
        dri-devel@...ts.freedesktop.org, arnd@...db.de,
        dmitry.baryshkov@....qualcomm.com
Subject: [PATCH v1 2/3] misc: fastrpc: Update context ID mask for polling mode support

Current fastrpc message context uses a 12-bit mask where the upper
8 bits are context ID from idr_alloc_cyclic and the lower 4 bits
represent PD type. This design works for normal fastrpc calls but
doesn't work as expected for polling mode. To enable polling mode
support from DSP(DSP writes to poll memory), DSP expects a 16-bit
context where the upper 8 bits are context ID, the lower 4 bits are
PD type and the 5th bit from the end denotes async mode(not yet
upstreamed). If this bit is set, DSP disables polling. With the
current design, odd context IDs set this bit, causing DSP to skip
poll memory updates. Update the context mask to ensure a hole
which won't get populated, ensuring polling mode works as expected.

Signed-off-by: Ekansh Gupta <ekansh.gupta@....qualcomm.com>
---
 drivers/misc/fastrpc.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index 0991ac487192..57e118de6e4a 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -37,7 +37,7 @@
 #define FASTRPC_CTX_MAX (256)
 #define FASTRPC_INIT_HANDLE	1
 #define FASTRPC_DSP_UTILITIES_HANDLE	2
-#define FASTRPC_CTXID_MASK (0xFF0)
+#define FASTRPC_CTXID_MASK (0xFF00)
 #define INIT_FILELEN_MAX (2 * 1024 * 1024)
 #define INIT_FILE_NAMELEN_MAX (128)
 #define FASTRPC_DEVICE_NAME	"fastrpc"
@@ -487,7 +487,7 @@ static void fastrpc_context_free(struct kref *ref)
 		fastrpc_buf_free(ctx->buf);
 
 	spin_lock_irqsave(&cctx->lock, flags);
-	idr_remove(&cctx->ctx_idr, ctx->ctxid >> 4);
+	idr_remove(&cctx->ctx_idr, ctx->ctxid >> 8);
 	spin_unlock_irqrestore(&cctx->lock, flags);
 
 	kfree(ctx->maps);
@@ -623,7 +623,7 @@ static struct fastrpc_invoke_ctx *fastrpc_context_alloc(
 		spin_unlock_irqrestore(&cctx->lock, flags);
 		goto err_idr;
 	}
-	ctx->ctxid = ret << 4;
+	ctx->ctxid = ret << 8;
 	spin_unlock_irqrestore(&cctx->lock, flags);
 
 	kref_init(&ctx->refcount);
@@ -2449,7 +2449,7 @@ static int fastrpc_rpmsg_callback(struct rpmsg_device *rpdev, void *data,
 	if (len < sizeof(*rsp))
 		return -EINVAL;
 
-	ctxid = ((rsp->ctx & FASTRPC_CTXID_MASK) >> 4);
+	ctxid = ((rsp->ctx & FASTRPC_CTXID_MASK) >> 8);
 
 	spin_lock_irqsave(&cctx->lock, flags);
 	ctx = idr_find(&cctx->ctx_idr, ctxid);
-- 
2.34.1