From: Armin Wolf
> Sent: 19 February 2022 21:10
>
> The new assembly code works on both 32 bit and 64 bit
> cpus and allows for more compiler optimisations by not
> requiring smm_regs to be packed. Also since the
> SMM handler seems to modify the carry flag, the new
> code informs the compiler that the flags register
> needs to be saved/restored. Since clang runs out of
> registers on 32 bit x86 when using CC_OUT, we need
> to execute "setc" ourself.
You always need to save anything from the flags register
inside the asm block - it is never valit afterwards.
> Also modify the debug message so we can still see
> the result (eax) when the carry flag was set.
>
> Tested with 32 bit and 64 bit kernels on a Dell Inspiron 3505.
>
> Signed-off-by: Armin Wolf <W_Armin@xxxxxx>
> ---
> Changes in v2:
> - fix clang running out of registers on 32 bit x86
> - modify debug message
> ---
> drivers/hwmon/dell-smm-hwmon.c | 85 ++++++++++------------------------
> 1 file changed, 25 insertions(+), 60 deletions(-)
>
> diff --git a/drivers/hwmon/dell-smm-hwmon.c b/drivers/hwmon/dell-smm-hwmon.c
> index c5939e68586d..f1538a46bfc9 100644
> --- a/drivers/hwmon/dell-smm-hwmon.c
> +++ b/drivers/hwmon/dell-smm-hwmon.c
> @@ -119,7 +119,7 @@ struct smm_regs {
> unsigned int edx;
> unsigned int esi;
> unsigned int edi;
> -} __packed;
> +};
>
> static const char * const temp_labels[] = {
> "CPU",
> @@ -165,73 +165,38 @@ static int i8k_smm_func(void *par)
> int eax = regs->eax;
> int ebx = regs->ebx;
> long long duration;
> - int rc;
> + bool carry;
I'd use an explicit 'unsigned char' not bool.
Matches the type of the 'setcc' instriction.
> /* SMM requires CPU 0 */
> if (smp_processor_id() != 0)
> return -EBUSY;
>
> -#if defined(CONFIG_X86_64)
> - asm volatile("pushq %%rax\n\t"
> - "movl 0(%%rax),%%edx\n\t"
> - "pushq %%rdx\n\t"
> - "movl 4(%%rax),%%ebx\n\t"
> - "movl 8(%%rax),%%ecx\n\t"
> - "movl 12(%%rax),%%edx\n\t"
> - "movl 16(%%rax),%%esi\n\t"
> - "movl 20(%%rax),%%edi\n\t"
> - "popq %%rax\n\t"
> - "out %%al,$0xb2\n\t"
> - "out %%al,$0x84\n\t"
> - "xchgq %%rax,(%%rsp)\n\t"
> - "movl %%ebx,4(%%rax)\n\t"
> - "movl %%ecx,8(%%rax)\n\t"
> - "movl %%edx,12(%%rax)\n\t"
> - "movl %%esi,16(%%rax)\n\t"
> - "movl %%edi,20(%%rax)\n\t"
> - "popq %%rdx\n\t"
> - "movl %%edx,0(%%rax)\n\t"
> - "pushfq\n\t"
> - "popq %%rax\n\t"
> - "andl $1,%%eax\n"
> - : "=a"(rc)
> - : "a"(regs)
> - : "%ebx", "%ecx", "%edx", "%esi", "%edi", "memory");
> -#else
> - asm volatile("pushl %%eax\n\t"
> - "movl 0(%%eax),%%edx\n\t"
> - "push %%edx\n\t"
> - "movl 4(%%eax),%%ebx\n\t"
> - "movl 8(%%eax),%%ecx\n\t"
> - "movl 12(%%eax),%%edx\n\t"
> - "movl 16(%%eax),%%esi\n\t"
> - "movl 20(%%eax),%%edi\n\t"
> - "popl %%eax\n\t"
> - "out %%al,$0xb2\n\t"
> - "out %%al,$0x84\n\t"
> - "xchgl %%eax,(%%esp)\n\t"
> - "movl %%ebx,4(%%eax)\n\t"
> - "movl %%ecx,8(%%eax)\n\t"
> - "movl %%edx,12(%%eax)\n\t"
> - "movl %%esi,16(%%eax)\n\t"
> - "movl %%edi,20(%%eax)\n\t"
> - "popl %%edx\n\t"
> - "movl %%edx,0(%%eax)\n\t"
> - "lahf\n\t"
> - "shrl $8,%%eax\n\t"
> - "andl $1,%%eax\n"
> - : "=a"(rc)
> - : "a"(regs)
> - : "%ebx", "%ecx", "%edx", "%esi", "%edi", "memory");
> -#endif
> - if (rc != 0 || (regs->eax & 0xffff) == 0xffff || regs->eax == eax)
> - rc = -EINVAL;
> + asm volatile("out %%al,$0xb2\n\t"
> + "out %%al,$0x84\n\t"
> + "setc %0\n"
> + : "=mr" (carry),
> + "=a" (regs->eax),
> + "=b" (regs->ebx),
> + "=c" (regs->ecx),
> + "=d" (regs->edx),
> + "=S" (regs->esi),
> + "=D" (regs->edi)
> + : "a" (regs->eax),
> + "b" (regs->ebx),
> + "c" (regs->ecx),
> + "d" (regs->edx),
> + "S" (regs->esi),
> + "D" (regs->edi)
If you use "+a" (etc) for the output registers you don't
need to respecify them as input registers.
> + : "cc");
No need to specify "cc", it is always assumed clobbered.
David
>
> duration = ktime_us_delta(ktime_get(), calltime);
> - pr_debug("smm(0x%.4x 0x%.4x) = 0x%.4x (took %7lld usecs)\n", eax, ebx,
> - (rc ? 0xffff : regs->eax & 0xffff), duration);
> + pr_debug("smm(0x%.4x 0x%.4x) = 0x%.4x carry: %d (took %7lld usecs)\n",
> + eax, ebx, regs->eax & 0xffff, carry, duration);
>
> - return rc;
> + if (carry || (regs->eax & 0xffff) == 0xffff || regs->eax == eax)
> + return -EINVAL;
> +
> + return 0;
> }
>
> /*
> --
> 2.30.2
-
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