>-----Original Message-----
>From: Kevin Hilman [mailto:khil...@deeprootsystems.com]
>Sent: Friday, June 05, 2009 4:54 AM
>To: Nayak, Rajendra
>Cc: linux-omap@vger.kernel.org
>Subject: Re: [PATCH 05/06] OMAP3: PM: Implement locking for
>any scratchpad access
>
>Rajendra Nayak <rna...@ti.com> writes:
>
>> This patch implements locking using the semaphore in scratchpad
>> memory preventing any concurrent access to scratchpad from OMAP
>> and Baseband/Modem processor.
>>
>> Signed-off-by: Rajendra Nayak <rna...@ti.com>
>
>Any reason this function has to be written in asm? It's written along
>with a bunch of other asm functions that are copied to and executed
>from SRAM, but that doesn't appear to be the case here.
>
>Looks like a simple C function would be clearer here.
Kevin,
The idea was to atomically read and write into the semaphore memory
location in scratchpad using a swp instruction.
I am not too sure how to do this in C.
regards,
Rajendra
>
>Kevin
>
>> ---
>> arch/arm/mach-omap2/resource34xx.c | 6 +++++-
>> arch/arm/mach-omap2/resource34xx.h | 2 ++
>> arch/arm/mach-omap2/sleep34xx.S | 32
>++++++++++++++++++++++++++++++++
>> 3 files changed, 39 insertions(+), 1 deletions(-)
>>
>> diff --git a/arch/arm/mach-omap2/resource34xx.c
>b/arch/arm/mach-omap2/resource34xx.c
>> index 82405b6..408d3ab 100644
>> --- a/arch/arm/mach-omap2/resource34xx.c
>> +++ b/arch/arm/mach-omap2/resource34xx.c
>> @@ -236,6 +236,7 @@ static int program_opp_freq(int res, int
>target_level, int current_level)
>> int ret = 0, l3_div;
>> int *curr_opp;
>>
>> + lock_scratchpad_sem();
>> if (res == VDD1_OPP) {
>> curr_opp = &curr_vdd1_opp;
>> clk_set_rate(dpll1_clk, mpu_opps[target_level].rate);
>> @@ -253,11 +254,14 @@ static int program_opp_freq(int res,
>int target_level, int current_level)
>> ret = clk_set_rate(dpll3_clk,
>> l3_opps[target_level].rate * l3_div);
>> }
>> - if (ret)
>> + if (ret) {
>> + unlock_scratchpad_sem();
>> return current_level;
>> + }
>> #ifdef CONFIG_PM
>> omap3_save_scratchpad_contents();
>> #endif
>> + unlock_scratchpad_sem();
>>
>> *curr_opp = target_level;
>> return target_level;
>> diff --git a/arch/arm/mach-omap2/resource34xx.h
>b/arch/arm/mach-omap2/resource34xx.h
>> index a160665..5b5618a 100644
>> --- a/arch/arm/mach-omap2/resource34xx.h
>> +++ b/arch/arm/mach-omap2/resource34xx.h
>> @@ -29,6 +29,8 @@
>> #include <mach/omap34xx.h>
>>
>> extern int sr_voltagescale_vcbypass(u32 t_opp, u32 c_opp,
>u8 t_vsel, u8 c_vsel);
>> +extern void lock_scratchpad_sem();
>> +extern void unlock_scratchpad_sem();
>>
>> /*
>> * mpu_latency/core_latency are used to control the cpuidle C state.
>> diff --git a/arch/arm/mach-omap2/sleep34xx.S
>b/arch/arm/mach-omap2/sleep34xx.S
>> index 38aa3fd..aedcf94 100644
>> --- a/arch/arm/mach-omap2/sleep34xx.S
>> +++ b/arch/arm/mach-omap2/sleep34xx.S
>> @@ -39,6 +39,7 @@
>> #define PM_PREPWSTST_MPU_V OMAP34XX_PRM_REGADDR(MPU_MOD, \
>> OMAP3430_PM_PREPWSTST)
>> #define CM_IDLEST1_CORE_V OMAP34XX_CM_REGADDR(CORE_MOD,
>CM_IDLEST1)
>> +#define SDRC_SCRATCHPAD_SEM_V 0xd800291C
>>
>> /*
>> * This is the physical address of the register as specified
>> @@ -62,6 +63,37 @@
>> #define SDRC_DLLA_STATUS_V OMAP34XX_SDRC_REGADDR(SDRC_DLLA_STATUS)
>> #define SDRC_DLLA_CTRL_V OMAP34XX_SDRC_REGADDR(SDRC_DLLA_CTRL)
>>
>> + .text
>> +/* Function to aquire the semaphore in scratchpad */
>> +ENTRY(lock_scratchpad_sem)
>> + stmfd sp!, {lr} @ save registers on stack
>> +wait_sem:
>> + mov r0,#1
>> + ldr r1, sdrc_scratchpad_sem
>> +wait_loop:
>> + ldr r2, [r1] @ load the lock value
>> + cmp r2, r0 @ is the lock free ?
>> + beq wait_loop @ not free...
>> + swp r2, r0, [r1] @ semaphore free so lock it and proceed
>> + cmp r2, r0 @ did we succeed ?
>> + beq wait_sem @ no - try again
>> + ldmfd sp!, {pc} @ restore regs and return
>> +sdrc_scratchpad_sem:
>> + .word SDRC_SCRATCHPAD_SEM_V
>> +ENTRY(lock_scratchpad_sem_sz)
>> + .word . - lock_scratchpad_sem
>> +
>> + .text
>> +/* Function to release the scratchpad semaphore */
>> +ENTRY(unlock_scratchpad_sem)
>> + stmfd sp!, {lr} @ save registers on stack
>> + ldr r3, sdrc_scratchpad_sem
>> + mov r2,#0
>> + str r2,[r3]
>> + ldmfd sp!, {pc} @ restore regs and return
>> +ENTRY(unlock_scratchpad_sem_sz)
>> + .word . - unlock_scratchpad_sem
>> +
>> .text
>> /* Function call to get the restore pointer for resume from OFF */
>> ENTRY(get_restore_pointer)
>> --
>> 1.5.4.7
>>
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