firmware: turris-mox-rwtm: Use macro constant instead of hardcoded 4096

The 4096 bytes limit in mox_hwrng_read() is due to the DMA buffer being
allocated to one PAGE_SIZE bytes. Use new local macro constant
RWTM_DMA_BUFFER_SIZE at allocation time and when used in mox_hwrng_read().

Use SZ_4K instead of PAGE_SIZE. Although PAGE_SIZE is never set to a
larger value on Armada 3720, it theoretically could, and this would be a
waste of space.

Signed-off-by: Marek Behún <kabel@kernel.org>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Link: https://lore.kernel.org/r/20240831092050.23093-2-kabel@kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

diff --git a/drivers/firmware/turris-mox-rwtm.c b/drivers/firmware/turris-mox-rwtm.c
index 3e7f186d239a2b774fced06a17a9116f3d272318..67d7b65da1741a7d9c25a3975ccf2ef17a5593eb 100644 (file)
--- a/drivers/firmware/turris-mox-rwtm.c
+++ b/drivers/firmware/turris-mox-rwtm.c
@@ -11,14 +11,18 @@
 #include <linux/dma-mapping.h>
 #include <linux/hw_random.h>
 #include <linux/mailbox_client.h>
+#include <linux/minmax.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/of.h>
 #include <linux/platform_device.h>
+#include <linux/sizes.h>
 #include <linux/slab.h>
 
 #define DRIVER_NAME            "turris-mox-rwtm"
 
+#define RWTM_DMA_BUFFER_SIZE   SZ_4K
+
 /*
  * The macros and constants below come from Turris Mox's rWTM firmware code.
  * This firmware is open source and it's sources can be found at
@@ -287,8 +291,7 @@ static int mox_hwrng_read(struct hwrng *rng, void *data, size_t max, bool wait)
        struct armada_37xx_rwtm_tx_msg msg;
        int ret;
 
-       if (max > 4096)
-               max = 4096;
+       max = min(max, RWTM_DMA_BUFFER_SIZE);
 
        msg.command = MBOX_CMD_GET_RANDOM;
        msg.args[0] = 1;
@@ -479,8 +482,8 @@ static int turris_mox_rwtm_probe(struct platform_device *pdev)
                return -ENOMEM;
 
        rwtm->dev = dev;
-       rwtm->buf = dmam_alloc_coherent(dev, PAGE_SIZE, &rwtm->buf_phys,
-                                       GFP_KERNEL);
+       rwtm->buf = dmam_alloc_coherent(dev, RWTM_DMA_BUFFER_SIZE,
+                                       &rwtm->buf_phys, GFP_KERNEL);
        if (!rwtm->buf)
                return -ENOMEM;