Hi, This series introduces a ti-emif-sram driver to be used on am335x and am437x. These SoCs have low power modes that require that the PER power domain be shut off. Because the EMIF (DDR Controller) resides within this power domain, it will lose context during a suspend operation, so we must save it so we can restore once we resume. However, we cannot execute this code from external memory, as it is not available at this point, so the code must be executed late in the suspend path and early in the resume path from SRAM. Patch 2 includes several functions written in ARM ASM that can be relocated to on-chip SRAM. It also exports a table containing the absolute addresses of the available PM functions so that other PM code also running from SRAM can branch to them. It must also calculate virtual addresses for the suspend path, but physical addresses for the resume path as the MMU is not active when the code runs. One thing that may not be immediately clear in the driver is that we can only get read-only exectuable memory regions from the mmio-sram driver so we also provide a second region to the driver that is read/write to be used for data during execution. This is the reason two sram regions are mapped and so many offsets must be provided to the code section. In order for structs to co-exist in C and ASM, I went ahead and extended the generic asm-offsets.c for ARM and added a single function call for this driver that adds all the constants needed for the ASM code to get offsets into the struct members. I managed to do it without many direct additions to the asm-offsets file so I do not think it is too intrusive. This was the only way I saw to do peaceful C and ASM data structure co-existence. Due to the dependencies of all of the code on this I did not not split ARM vs drivers/ changes into separate patches because I think it would be more confusing that way but if needed I think it can be done. This code is required for low-power modes to work on AM335x and AM437x and a forthcoming PM series for those platforms will depend on this series. After both this and the PM series are reviewed I will send the necessary device tree changes for both, but in the meantime all remaining patches for am335x and am437x PM can be found here [1]. Regards, Dave [1] https://github.com/dgerlach/linux-pm/tree/upstream/v4.11/amx3-suspend-dev Dave Gerlach (2): Documentation: dt: Update ti,emif bindings memory: ti-emif-sram: introduce relocatable suspend/resume handlers .../bindings/memory-controllers/ti/emif.txt | 18 +- arch/arm/kernel/asm-offsets.c | 6 + drivers/memory/Kconfig | 10 + drivers/memory/Makefile | 4 + drivers/memory/emif.h | 17 ++ drivers/memory/ti-emif-pm.c | 295 ++++++++++++++++++ drivers/memory/ti-emif-sram-pm.S | 334 +++++++++++++++++++++ include/linux/ti-emif-sram.h | 143 +++++++++ 8 files changed, 826 insertions(+), 1 deletion(-) create mode 100644 drivers/memory/ti-emif-pm.c create mode 100644 drivers/memory/ti-emif-sram-pm.S create mode 100644 include/linux/ti-emif-sram.h -- 2.11.0 -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
