firmware: arm_ffa: Respect firmware advertised RX/TX buffer size limits

FFA_FEATURES reports the minimum size and alignment boundary required
for RXTX_MAP. In FF-A v1.2 and later it can also report a maximum buffer
size, with zero meaning that no maximum is enforced.

The driver only used the minimum value and then rounded it up to PAGE_SIZE
before invoking RXTX_MAP after commit 83210251fd70 ("firmware: arm_ffa:
Use the correct buffer size during RXTX_MAP"). On systems where PAGE_SIZE
is larger than the advertised minimum, this can exceed a non-zero maximum
reported by firmware. Older implementations do not advertise a maximum and
may also reject the rounded-up size.

Decode the maximum size and clamp the page-aligned minimum to it when it
is present. If no maximum is advertised and RXTX_MAP rejects the rounded
size with INVALID_PARAMETERS, retry with the advertised minimum size.
Record drv_info->rxtx_bufsz only after RXTX_MAP succeeds so it reflects
the size registered with firmware.

While there, also update RXTX_MAP_MIN_BUFSZ() to use FIELD_GET() for
consistency.

Fixes: 83210251fd70 ("firmware: arm_ffa: Use the correct buffer size during RXTX_MAP")
Suggested-by: Sudeep Holla <sudeep.holla@kernel.org>
Signed-off-by: Seth Forshee <sforshee@nvidia.com>
Link: https://patch.msgid.link/20260602-b4-ffa-rxtx-map-fixes-v2-1-7cb06508da84@nvidia.com
(sudeep.holla: Minor rewording subject and commit message)
Signed-off-by: Sudeep Holla <sudeep.holla@kernel.org>

1 files changed, 20 insertions, 7 deletions

diff --git a/drivers/firmware/arm_ffa/driver.c b/drivers/firmware/arm_ffa/driver.c
index 0f468362c288..bc2685331b27 100644
--- a/drivers/firmware/arm_ffa/driver.c
+++ b/drivers/firmware/arm_ffa/driver.c
@@ -32,6 +32,7 @@
 #include <linux/interrupt.h>
 #include <linux/io.h>
 #include <linux/kernel.h>
+#include <linux/minmax.h>
 #include <linux/module.h>
 #include <linux/mm.h>
 #include <linux/mutex.h>
@@ -59,7 +60,9 @@
 	(FIELD_PREP(SENDER_ID_MASK, (s)) | FIELD_PREP(RECEIVER_ID_MASK, (r)))
 
 #define RXTX_MAP_MIN_BUFSZ_MASK	GENMASK(1, 0)
-#define RXTX_MAP_MIN_BUFSZ(x)	((x) & RXTX_MAP_MIN_BUFSZ_MASK)
+#define RXTX_MAP_MAX_BUFSZ_MASK	GENMASK(31, 16)
+#define RXTX_MAP_MIN_BUFSZ(x)	(FIELD_GET(RXTX_MAP_MIN_BUFSZ_MASK, (x)))
+#define RXTX_MAP_MAX_BUFSZ(x)	(FIELD_GET(RXTX_MAP_MAX_BUFSZ_MASK, (x)))
 
 #define FFA_MAX_NOTIFICATIONS		64
 
@@ -2101,7 +2104,7 @@ static int ffa_probe(struct platform_device *pdev)
 {
 	int ret;
 	u32 buf_sz;
-	size_t rxtx_bufsz = SZ_4K;
+	size_t rxtx_min_bufsz = SZ_4K, rxtx_max_bufsz = 0, rxtx_bufsz;
 
 	if (IS_BUILTIN(CONFIG_ARM_FFA_TRANSPORT) &&
 	    is_protected_kvm_enabled() && !is_pkvm_initialized())
@@ -2132,15 +2135,18 @@ static int ffa_probe(struct platform_device *pdev)
 	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;
+
+		rxtx_max_bufsz = RXTX_MAP_MAX_BUFSZ(buf_sz) * SZ_4K;
+		if (rxtx_max_bufsz != 0 && rxtx_max_bufsz < rxtx_min_bufsz)
+			rxtx_max_bufsz = rxtx_min_bufsz;
 	}
 
-	rxtx_bufsz = PAGE_ALIGN(rxtx_bufsz);
-	drv_info->rxtx_bufsz = rxtx_bufsz;
+	rxtx_bufsz = min_not_zero(PAGE_ALIGN(rxtx_min_bufsz), rxtx_max_bufsz);
 	drv_info->rx_buffer = alloc_pages_exact(rxtx_bufsz, GFP_KERNEL);
 	if (!drv_info->rx_buffer) {
 		ret = -ENOMEM;
@@ -2156,10 +2162,17 @@ static int ffa_probe(struct platform_device *pdev)
 	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 && rxtx_min_bufsz < rxtx_bufsz) {
+		rxtx_bufsz = rxtx_min_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;
 	}
+	drv_info->rxtx_bufsz = rxtx_bufsz;
 
 	mutex_init(&drv_info->rx_lock);
 	mutex_init(&drv_info->tx_lock);