[PATCH 2/2] firmware: arm_ffa: Fall back to minimum buffer size if RXTX_MAP fails

[Seth Forshee <sforshee@nvidia.com>]

FFA_FEATURES only supports a maximum size value for RXTX_MAP in v1.2+.
Older implementations may still reject larger sizes, which can happen
when the minimum size is rounded up to the page size when PAGE_SIZE >
4K.

Fall back to the minimum size when RXTX_MAP fails with
INVALID_PARAMETERS to fix the regression on these platforms. This also
has the side effect of falling back for v1.2+ with a maximum of 0 (i.e.
no maximum), where the rounded-up value isn't expected to be rejected,
but there's no harm in retrying with a smaller size and it might even be
of benefit for a non-compliant SPMC.

Note that this may result in passing a size smaller than the allocated
size to free_pages_exact(). This does not result in any leaked memory,
since the size extends into all allocated pages, and free_pages_exact()
correctly handles sizes which are not page aligned.

Fixes: 83210251fd70 ("firmware: arm_ffa: Use the correct buffer size during RXTX_MAP")
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Seth Forshee <sforshee@nvidia.com>
---
 drivers/firmware/arm_ffa/driver.c | 28 +++++++++++++++++++++-------
 1 file changed, 21 insertions(+), 7 deletions(-)

diff --git a/drivers/firmware/arm_ffa/driver.c b/drivers/firmware/arm_ffa/driver.c
index dc45724a29ba..60ad58e229ce 100644
--- a/drivers/firmware/arm_ffa/driver.c
+++ b/drivers/firmware/arm_ffa/driver.c
@@ -2095,7 +2095,7 @@ static int __init ffa_init(void)
 {
 	int ret;
 	u32 buf_sz;
-	size_t rxtx_bufsz = SZ_4K, rxtx_max_bufsz = 0;
+	size_t rxtx_min_bufsz = SZ_4K, rxtx_max_bufsz = 0, rxtx_bufsz;
 
 	ret = ffa_transport_init(&invoke_ffa_fn);
 	if (ret)
@@ -2118,22 +2118,22 @@ static int __init ffa_init(void)
 	ret = ffa_features(FFA_FN_NATIVE(RXTX_MAP), 0, &buf_sz, NULL);
 	if (!ret) {
 		if (RXTX_MAP_MIN_BUFSZ(buf_sz) == 1)
-			rxtx_bufsz = SZ_64K;
+			rxtx_min_bufsz = SZ_64K;
 		else if (RXTX_MAP_MIN_BUFSZ(buf_sz) == 2)
-			rxtx_bufsz = SZ_16K;
+			rxtx_min_bufsz = SZ_16K;
 		else
-			rxtx_bufsz = SZ_4K;
+			rxtx_min_bufsz = SZ_4K;
 
 		if (FFA_SUPPORTS_RXTX_MAX_BUFSZ(drv_info->version)) {
 			rxtx_max_bufsz = (size_t)RXTX_MAP_MAX_BUFSZ(buf_sz) * SZ_4K;
-			if (rxtx_max_bufsz != 0 && rxtx_max_bufsz < rxtx_bufsz) {
+			if (rxtx_max_bufsz != 0 && rxtx_max_bufsz < rxtx_min_bufsz) {
 				/*
 				 * Per spec the maximum must be >= the minimum, or
 				 * else zero if there is no size limit. If the SPMC
 				 * violates this constraint, use the minimum as the
 				 * effective maximum.
 				 */
-				rxtx_max_bufsz = rxtx_bufsz;
+				rxtx_max_bufsz = rxtx_min_bufsz;
 			}
 		}
 	}
@@ -2142,7 +2142,7 @@ static int __init ffa_init(void)
 	 * alloc_pages_exact() allocates full pages. Use the full allocated
 	 * space up to the max supported by the SPMC.
 	 */
-	rxtx_bufsz = PAGE_ALIGN(rxtx_bufsz);
+	rxtx_bufsz = PAGE_ALIGN(rxtx_min_bufsz);
 	if (rxtx_max_bufsz)
 		rxtx_bufsz = min(rxtx_bufsz, rxtx_max_bufsz);
 
@@ -2162,6 +2162,20 @@ static int __init ffa_init(void)
 	ret = ffa_rxtx_map(virt_to_phys(drv_info->tx_buffer),
 			   virt_to_phys(drv_info->rx_buffer),
 			   rxtx_bufsz / FFA_PAGE_SIZE);
+	if (ret == -EINVAL && rxtx_max_bufsz == 0 && rxtx_min_bufsz < rxtx_bufsz) {
+		/*
+		 * FFA_FEATURES only supports maximum buffer size in v1.2+,
+		 * and some implementations without it may fail when the
+		 * buffer size is rounded up to a larger page size. If
+		 * RXTX_MAP fails due to invalid parameters, try again with
+		 * the minimum buffer size.
+		 */
+		rxtx_bufsz = rxtx_min_bufsz;
+		drv_info->rxtx_bufsz = rxtx_bufsz;
+		ret = ffa_rxtx_map(virt_to_phys(drv_info->tx_buffer),
+				   virt_to_phys(drv_info->rx_buffer),
+				   rxtx_bufsz / FFA_PAGE_SIZE);
+	}
 	if (ret) {
 		pr_err("failed to register FFA RxTx buffers\n");
 		goto free_pages;

-- 
2.43.0