netdev - [PATCH net-next v3 4/4] net: ipa: relax 64-bit build requirement

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Date:   Thu, 18 Mar 2021 13:59:30 -0500
From:   Alex Elder <elder@...aro.org>
To:     davem@...emloft.net, kuba@...nel.org
Cc:     f.fainelli@...il.com, bjorn.andersson@...aro.org,
        evgreen@...omium.org, cpratapa@...eaurora.org,
        subashab@...eaurora.org, elder@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH net-next v3 4/4] net: ipa: relax 64-bit build requirement

We currently assume the IPA driver is built only for a 64 bit kernel.

When this constraint was put in place it eliminated some do_div()
calls, replacing them with the "/" and "%" operators.  We now only
use these operations on u32 and size_t objects.  In a 32-bit kernel
build, size_t will be 32 bits wide, so there remains no reason to
use do_div() for divide and modulo.

A few recent commits also fix some code that assumes that DMA
addresses are 64 bits wide.

With that, we can get rid of the 64-bit build requirement.

Signed-off-by: Alex Elder <elder@...aro.org>
---
 drivers/net/ipa/Kconfig    |  2 +-
 drivers/net/ipa/ipa_main.c | 10 ++++++++--
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ipa/Kconfig b/drivers/net/ipa/Kconfig
index b68f1289b89ef..90a90262e0d07 100644
--- a/drivers/net/ipa/Kconfig
+++ b/drivers/net/ipa/Kconfig
@@ -1,6 +1,6 @@
 config QCOM_IPA
 	tristate "Qualcomm IPA support"
-	depends on 64BIT && NET && QCOM_SMEM
+	depends on NET && QCOM_SMEM
 	depends on ARCH_QCOM || COMPILE_TEST
 	depends on QCOM_RPROC_COMMON || (QCOM_RPROC_COMMON=n && COMPILE_TEST)
 	select QCOM_MDT_LOADER if ARCH_QCOM
diff --git a/drivers/net/ipa/ipa_main.c b/drivers/net/ipa/ipa_main.c
index 97c1b55405cbf..d354e3e65ec50 100644
--- a/drivers/net/ipa/ipa_main.c
+++ b/drivers/net/ipa/ipa_main.c
@@ -735,8 +735,14 @@ MODULE_DEVICE_TABLE(of, ipa_match);
 static void ipa_validate_build(void)
 {
 #ifdef IPA_VALIDATE
-	/* We assume we're working on 64-bit hardware */
-	BUILD_BUG_ON(!IS_ENABLED(CONFIG_64BIT));
+	/* At one time we assumed a 64-bit build, allowing some do_div()
+	 * calls to be replaced by simple division or modulo operations.
+	 * We currently only perform divide and modulo operations on u32,
+	 * u16, or size_t objects, and of those only size_t has any chance
+	 * of being a 64-bit value.  (It should be guaranteed 32 bits wide
+	 * on a 32-bit build, but there is no harm in verifying that.)
+	 */
+	BUILD_BUG_ON(!IS_ENABLED(CONFIG_64BIT) && sizeof(size_t) != 4);
 
 	/* Code assumes the EE ID for the AP is 0 (zeroed structure field) */
 	BUILD_BUG_ON(GSI_EE_AP != 0);
-- 
2.27.0