* Russell King - ARM Linux <linux@xxxxxxxxxxxxxxx> [170405 07:02]: > On Tue, Apr 04, 2017 at 09:11:52AM -0700, Tony Lindgren wrote: > > Russell, > > > > * Dave Gerlach <d-gerlach@xxxxxx> [170328 13:57]: > > > Certain SoCs like Texas Instruments AM335x and AM437x require parts > > > of the EMIF PM code to run late in the suspend sequence from SRAM, > > > such as saving and restoring the EMIF context and placing the memory > > > into self-refresh. > > > > > > One requirement for these SoCs to suspend and enter its lowest power > > > mode, called DeepSleep0, is that the PER power domain must 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 from SRAM. > > > > > > This patch introduces a ti-emif-sram driver that includes several > > > functions written in ARM ASM that are relocatable so the PM SRAM > > > code can use them. It also allocates a region of writable SRAM to > > > be used by the code running in the executable region of SRAM to save > > > and restore the EMIF context. It can export a table containing the > > > absolute addresses of the available PM functions so that other SRAM > > > code can branch to them. This code is required for suspend/resume on > > > AM335x and AM437x to work. > > > > > > In addition to this, to be able to share data structures between C and > > > the ti-emif-sram-pm assembly code, we can automatically generate all of > > > the C struct member offsets and sizes as macros by making use of the ARM > > > asm-offsets file. In the same header that we define our data structures > > > in we also define all the macros in an inline function and by adding a > > > call to this in the asm_offsets file all macros are properly generated > > > and available to the assembly code without cluttering up the asm-offsets > > > file. > > > > > > Signed-off-by: Dave Gerlach <d-gerlach@xxxxxx> > > > --- > > > 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 +++++++++++++++++ > > > 7 files changed, 809 insertions(+) > > > 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 > > > > > > diff --git a/arch/arm/kernel/asm-offsets.c b/arch/arm/kernel/asm-offsets.c > > > index 608008229c7d..d728b5660e36 100644 > > > --- a/arch/arm/kernel/asm-offsets.c > > > +++ b/arch/arm/kernel/asm-offsets.c > > > @@ -28,6 +28,7 @@ > > > #include <asm/vdso_datapage.h> > > > #include <asm/hardware/cache-l2x0.h> > > > #include <linux/kbuild.h> > > > +#include <linux/ti-emif-sram.h> > > > > > > /* > > > * Make sure that the compiler and target are compatible. > > > @@ -183,5 +184,10 @@ int main(void) > > > #ifdef CONFIG_VDSO > > > DEFINE(VDSO_DATA_SIZE, sizeof(union vdso_data_store)); > > > #endif > > > +#if defined(CONFIG_SOC_AM33XX) || defined(CONFIG_SOC_AM43XX) > > > + BLANK(); > > > + ti_emif_offsets(); > > > +#endif > > > + > > > return 0; > > > } > > > > Does the above look OK to you? > > I'm not going to comment on this yet, but I'll instead comment on the > newly appeared sram_exec_copy() stuff. > > So, a few years ago, we went to significant effort in ARM land to come > up with a way to _safely_ copy assembler from the kernel into SRAM, > because copying code to SRAM that is compiled in thumb mode and then > executing it is _not_ as simple as memcpy(), cast the pointer to a > function pointer, and then call the function pointer. > > The SRAM stuff throws all that out, instead preferring the dumb memcpy() > approach. > > This needs resolving, and I'd like to see it resolved to the satisfaction > of architecture maintainers before we progress any further down this > route. OK thanks, will wait until that is sorted out before merging any of the SRAM code. Regards, Tony -- 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
