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From:   <cristian.birsan@microchip.com>
To:     <arnd@arndb.de>, <olof@lixom.net>, <soc@kernel.org>,
        <robh+dt@kernel.org>, <krzysztof.kozlowski+dt@linaro.org>,
        <conor+dt@kernel.org>
CC:     <linux-arm-kernel@lists.infradead.org>,
        <devicetree@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        Cristian Birsan <cristian.birsan@microchip.com>
Subject: [PATCH] arm: dts: Enable device-tree overlay support for AT91 boards
Date:   Fri, 16 Jun 2023 18:29:32 +0300
Message-ID: <20230616152932.1484154-1-cristian.birsan@microchip.com>
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From: Cristian Birsan <cristian.birsan@microchip.com>

Add the '-@' DTC option for AT91 boards that have device-tree overlays.
This option populates the '__symbols__' node that contains all the
necessary symbols for supporting device-tree overlays (from bootloader)
on these devices.

This change increases the size of the resulting DTB with ~30%-40%. Below
are the measurements performed v6.4-rc6:

at91-sam9x60_curiosity.dtb	28499 -> 36641 bytes
at91-sam9x60ek.dtb		30867 -> 39609 bytes
at91-sama5d27_som1_ek.dtb	26086 -> 34166 bytes
at91-sama5d27_wlsom1_ek.dtb	26045 -> 33184 bytes
at91-sama5d2_icp.dtb		27521 -> 36155 bytes
at91-sama5d2_ptc_ek.dtb		23237 -> 29612 bytes
at91-sama5d2_xplained.dtb	27262 -> 35326 bytes
at91-sama5d3_eds.dtb		27924 -> 39939 bytes
at91-sama5d3_xplained.dtb	28400 -> 40650 bytes
at91-sama5d4_xplained.dtb	26456 -> 36107 bytes
at91-sama7g5ek.dtb		29212 -> 37289 bytes

Signed-off-by: Cristian Birsan <cristian.birsan@microchip.com>
---
 arch/arm/boot/dts/Makefile | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/arm/boot/dts/Makefile b/arch/arm/boot/dts/Makefile
index 59829fc90315..38b82af2bf69 100644
--- a/arch/arm/boot/dts/Makefile
+++ b/arch/arm/boot/dts/Makefile
@@ -50,9 +50,21 @@ dtb-$(CONFIG_SOC_AT91SAM9) += \
 	at91sam9g35ek.dtb \
 	at91sam9x25ek.dtb \
 	at91sam9x35ek.dtb
+# Enables support for device-tree overlays
+DTC_FLAGS_at91-sam9x60_curiosity := -@
+DTC_FLAGS_at91-sam9x60ek := -@
 dtb-$(CONFIG_SOC_SAM9X60) += \
 	at91-sam9x60_curiosity.dtb \
 	at91-sam9x60ek.dtb
+# Enables support for device-tree overlays
+DTC_FLAGS_at91-sama5d27_som1_ek := -@
+DTC_FLAGS_at91-sama5d27_wlsom1_ek := -@
+DTC_FLAGS_at91-sama5d2_icp := -@
+DTC_FLAGS_at91-sama5d2_ptc_ek := -@
+DTC_FLAGS_at91-sama5d2_xplained := -@
+DTC_FLAGS_at91-sama5d3_eds := -@
+DTC_FLAGS_at91-sama5d3_xplained := -@
+DTC_FLAGS_at91-sama5d4_xplained := -@
 dtb-$(CONFIG_SOC_SAM_V7) += \
 	at91-kizbox2-2.dtb \
 	at91-kizbox3-hs.dtb \
@@ -79,6 +91,8 @@ dtb-$(CONFIG_SOC_SAM_V7) += \
 	at91-sama5d4_xplained.dtb \
 	at91-sama5d4ek.dtb \
 	at91-vinco.dtb
+# Enables support for device-tree overlays
+DTC_FLAGS_at91-sama7g5ek := -@
 dtb-$(CONFIG_SOC_SAMA7G5) += \
 	at91-sama7g5ek.dtb
 dtb-$(CONFIG_SOC_SP7021) += \
-- 
2.34.1