crypto: stm32/crc32 - Avoid lock if hardware is already used

If STM32 CRC device is already in use, calculate CRC by software.

This will release CPU constraint for a concurrent access to the
hardware, and avoid masking irqs during the whole block processing.

Fixes: 7795c0ba ("crypto: stm32/crc32 - protect from concurrent accesses")
Signed-off-by: Nicolas Toromanoff <nicolas.toromanoff@st.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/stm32/Kconfig

@@ -3,6 +3,7 @@ config CRYPTO_DEV_STM32_CRC
 	tristate "Support for STM32 crc accelerators"
 	depends on ARCH_STM32
 	select CRYPTO_HASH
+	select CRC32
 	help
 	  This enables support for the CRC32 hw accelerator which can be found
 	  on STMicroelectronics STM32 SOC.

drivers/crypto/stm32/stm32-crc32.c

@@ -6,6 +6,7 @@
 
 #include <linux/bitrev.h>
 #include <linux/clk.h>
+#include <linux/crc32.h>
 #include <linux/crc32poly.h>
 #include <linux/io.h>
 #include <linux/kernel.h>
@@ -149,7 +150,6 @@ static int burst_update(struct shash_desc *desc, const u8 *d8,
 	struct stm32_crc_desc_ctx *ctx = shash_desc_ctx(desc);
 	struct stm32_crc_ctx *mctx = crypto_shash_ctx(desc->tfm);
 	struct stm32_crc *crc;
-	unsigned long flags;
 
 	crc = stm32_crc_get_next_crc();
 	if (!crc)
@@ -157,7 +157,15 @@ static int burst_update(struct shash_desc *desc, const u8 *d8,
 
 	pm_runtime_get_sync(crc->dev);
 
-	spin_lock_irqsave(&crc->lock, flags);
+	if (!spin_trylock(&crc->lock)) {
+		/* Hardware is busy, calculate crc32 by software */
+		if (mctx->poly == CRC32_POLY_LE)
+			ctx->partial = crc32_le(ctx->partial, d8, length);
+		else
+			ctx->partial = __crc32c_le(ctx->partial, d8, length);
+
+		goto pm_out;
+	}
 
 	/*
 	 * Restore previously calculated CRC for this context as init value
@@ -197,8 +205,9 @@ static int burst_update(struct shash_desc *desc, const u8 *d8,
 	/* Store partial result */
 	ctx->partial = readl_relaxed(crc->regs + CRC_DR);
 
-	spin_unlock_irqrestore(&crc->lock, flags);
+	spin_unlock(&crc->lock);
 
+pm_out:
 	pm_runtime_mark_last_busy(crc->dev);
 	pm_runtime_put_autosuspend(crc->dev);