linux-kernel - Re: [PATCH V3] irqchip:gic: change access of gicc

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Date:	Tue, 9 Sep 2014 11:31:49 +0530
From:	Arun Chandran <achandran@...sta.com>
To:	Feng Kan <fkan@....com>
Cc:	"tglx@...utronix.de" <tglx@...utronix.de>,
	patches <patches@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Marc Zyngier <marc.zyngier@....com>,
	Vinayak Kale <vkale@....com>
Subject: Re: [PATCH V3] irqchip:gic: change access of gicc_ctrl register to
 read modify write.

On Mon, Sep 8, 2014 at 10:27 PM, Feng Kan <fkan@....com> wrote:
> On Mon, Sep 8, 2014 at 1:52 AM, Arun Chandran <achandran@...sta.com> wrote:
>> Hi Feng,
>>
>> Is this patch still needed to fix perf calltrace?
> Yes, if the someone decide to run the secure mode of the GIC, which is
> what is present in
> the kernel tree now.
>
>> http://lists.infradead.org/pipermail/linux-arm-kernel/2014-June/265814.html
>>
>> On Fri, Feb 28, 2014 at 3:06 AM, Feng Kan <fkan@....com> wrote:
>>> This change is made to preserve the GIC v2 releated bits in the
>>> GIC_CPU_CTRL register (also known as the GICC_CTLR register in spec).
>>> The original code only set the enable/disable group bit in this register.
>>> This code will preserve the bypass bits configured by the bootload except
>>> the enable/disable bit. The main reason for this change is to allow the
>>> bypass bits specified in the v2 spec to remain untouched by the current
>>> GIC code. In the X-Gene platform, the bypass functionality is not used
>>> and bypass must be disabled at all time.
>>>
>>> Signed-off-by: Vinayak Kale <vkale@....com>
>>> Acked-by: Anup Patel <apatel@....com>
>>> Signed-off-by: Feng Kan <fkan@....com>
>>> ---
>>> V3 Changes:
>>>         - Sorry, forgot to change the mask for cpu_init path
>>>           assumed bootloader setup bits correctly.
>>> V2 Changes:
>>>         - only mask off v2 bypass bits
>>>  drivers/irqchip/irq-gic.c |   32 +++++++++++++++++++++++++++++---
>>>  1 files changed, 29 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
>>> index 341c601..3ca7995 100644
>>> --- a/drivers/irqchip/irq-gic.c
>>> +++ b/drivers/irqchip/irq-gic.c
>>> @@ -418,6 +418,7 @@ static void gic_cpu_init(struct gic_chip_data *gic)
>>>         void __iomem *dist_base = gic_data_dist_base(gic);
>>>         void __iomem *base = gic_data_cpu_base(gic);
>>>         unsigned int cpu_mask, cpu = smp_processor_id();
>>> +       unsigned int ctrl_mask;
>>>         int i;
>>>
>>>         /*
>>> @@ -449,13 +450,29 @@ static void gic_cpu_init(struct gic_chip_data *gic)
>>>                 writel_relaxed(0xa0a0a0a0, dist_base + GIC_DIST_PRI + i * 4 / 4);
>>>
>>>         writel_relaxed(0xf0, base + GIC_CPU_PRIMASK);
>>> -       writel_relaxed(1, base + GIC_CPU_CTRL);
>>> +
>>> +       ctrl_mask = readl(base + GIC_CPU_CTRL);
>>
>> readl_relaxed() here?
>>
>>> +
>>> +       /* Mask out the gic v2 bypass bits */
>>> +       ctrl_mask &= 0x1e0;
>>> +
>>> +       /* Enable group 0 */
>>> +       ctrl_mask |= 0x1;
>>> +       writel_relaxed(ctrl_mask, base + GIC_CPU_CTRL);
>>>  }
>>>
>>>  void gic_cpu_if_down(void)
>>>  {
>>> +       unsigned int ctrl_mask;
>>>         void __iomem *cpu_base = gic_data_cpu_base(&gic_data[0]);
>>> -       writel_relaxed(0, cpu_base + GIC_CPU_CTRL);
>>> +
>>> +       ctrl_mask = readl(cpu_base + GIC_CPU_CTRL);
>> readl_relaxed() here?
>>
>>> +       /*
>>> +        * Disable grp enable bit, leave the bypass bits alone as changing
>>> +        * them could leave the system unstable
>>> +        */
>>> +       ctrl_mask &= 0x1e0;
>>> +       writel_relaxed(ctrl_mask, cpu_base + GIC_CPU_CTRL);
>>>  }
>>>
>>>  #ifdef CONFIG_CPU_PM
>>> @@ -566,6 +583,7 @@ static void gic_cpu_restore(unsigned int gic_nr)
>>>  {
>>>         int i;
>>>         u32 *ptr;
>>> +       unsigned int ctrl_mask;
>>>         void __iomem *dist_base;
>>>         void __iomem *cpu_base;
>>>
>>> @@ -590,7 +608,15 @@ static void gic_cpu_restore(unsigned int gic_nr)
>>>                 writel_relaxed(0xa0a0a0a0, dist_base + GIC_DIST_PRI + i * 4);
>>>
>>>         writel_relaxed(0xf0, cpu_base + GIC_CPU_PRIMASK);
>>> -       writel_relaxed(1, cpu_base + GIC_CPU_CTRL);
>>> +
>>> +       ctrl_mask = readl(cpu_base + GIC_CPU_CTRL);
>>
>> readl_relaxed() here?
> Trying to make sure read is completed before write back out to gic.
>>

Will the cpu reorder  readl_relaxed() and a writel_relaxed() calls?

val = readl_relaxed(reg1);
val += 1;
wrietl_relaxed(val, reg1);

In the above code reg1 getting 'val+1' is not guaranteed?

--Arun
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