This is a note to let you know that I've just added the patch titled cpufreq: speedstep-smi: enable interrupts when waiting to the 3.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: cpufreq-speedstep-smi-enable-interrupts-when-waiting.patch and it can be found in the queue-3.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From d4d4eda23794c701442e55129dd4f8f2fefd5e4d Mon Sep 17 00:00:00 2001 From: Mikulas Patocka <mpatocka@xxxxxxxxxx> Date: Mon, 9 Feb 2015 13:38:17 -0500 Subject: cpufreq: speedstep-smi: enable interrupts when waiting From: Mikulas Patocka <mpatocka@xxxxxxxxxx> commit d4d4eda23794c701442e55129dd4f8f2fefd5e4d upstream. On Dell Latitude C600 laptop with Pentium 3 850MHz processor, the speedstep-smi driver sometimes loads and sometimes doesn't load with "change to state X failed" message. The hardware sometimes refuses to change frequency and in this case, we need to retry later. I found out that we need to enable interrupts while waiting. When we enable interrupts, the hardware blockage that prevents frequency transition resolves and the transition is possible. With disabled interrupts, the blockage doesn't resolve (no matter how long do we wait). The exact reasons for this hardware behavior are unknown. This patch enables interrupts in the function speedstep_set_state that can be called with disabled interrupts. However, this function is called with disabled interrupts only from speedstep_get_freqs, so it shouldn't cause any problem. Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/cpufreq/speedstep-lib.c | 3 +++ drivers/cpufreq/speedstep-smi.c | 12 ++++++++++++ 2 files changed, 15 insertions(+) --- a/drivers/cpufreq/speedstep-lib.c +++ b/drivers/cpufreq/speedstep-lib.c @@ -400,6 +400,7 @@ unsigned int speedstep_get_freqs(enum sp pr_debug("previous speed is %u\n", prev_speed); + preempt_disable(); local_irq_save(flags); /* switch to low state */ @@ -464,6 +465,8 @@ unsigned int speedstep_get_freqs(enum sp out: local_irq_restore(flags); + preempt_enable(); + return ret; } EXPORT_SYMBOL_GPL(speedstep_get_freqs); --- a/drivers/cpufreq/speedstep-smi.c +++ b/drivers/cpufreq/speedstep-smi.c @@ -156,6 +156,7 @@ static void speedstep_set_state(unsigned return; /* Disable IRQs */ + preempt_disable(); local_irq_save(flags); command = (smi_sig & 0xffffff00) | (smi_cmd & 0xff); @@ -166,9 +167,19 @@ static void speedstep_set_state(unsigned do { if (retry) { + /* + * We need to enable interrupts, otherwise the blockage + * won't resolve. + * + * We disable preemption so that other processes don't + * run. If other processes were running, they could + * submit more DMA requests, making the blockage worse. + */ pr_debug("retry %u, previous result %u, waiting...\n", retry, result); + local_irq_enable(); mdelay(retry * 50); + local_irq_disable(); } retry++; __asm__ __volatile__( @@ -185,6 +196,7 @@ static void speedstep_set_state(unsigned /* enable IRQs */ local_irq_restore(flags); + preempt_enable(); if (new_state == state) pr_debug("change to %u MHz succeeded after %u tries " Patches currently in stable-queue which might be from mpatocka@xxxxxxxxxx are queue-3.14/cpufreq-speedstep-smi-enable-interrupts-when-waiting.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html