[PATCH v2] Added perf functionality to mmdc driver

[Nitin Chaudhary]

Hi Zhengyu,

There are two main reasons why I made pmu_mmdc to be static:
1. Since i.MX6Q has only a single MMDC IP, at any time there should be
only 1 instance of the same.
2. Now as the code plugs itself into the perf core, it is very
unlikely we need to allow access to this
 data structure from outside the driver code. If we need to do for
some reasons in kernel in the future then
 we can expose some wrapper APIs to achieve that in a safeway.

Also, I have a few questions regarding MMDC initialization.
1. Is there any specific hardware initialization reason that we do a
busy loop while trying to enable Automatic
    power saving mode. Is it possible to move it to deferred workqueue?
2. I am having an issue with the MMDC driver running Linux Kernel
4.8-rc2 and its unable to successfully
    probe due to timeout waiting for MMDC automatic wait getting
enabled. The below is the log message
    along with the debug messages I added to dump the read values for
MDMIC and MAPSR reg in MMDC
   connected to singel channel DDR3.
[    0.133162] imx_mmdc_probe MMDC_MDMISC: 0x40001740
[    0.133178] imx_mmdc_probe MMDC_MAPSR: 0x00001046 << Before
[    0.133871] imx_mmdc_probe: failed to enable automatic power saving
[    0.133969] imx-mmdc 21b0000.mmdc: No access to interrupts, using timer.

The code snippet where the debug logs are printed is as below:
static int imx_mmdc_probe(struct platform_device *pdev)
<snip>
        val = readl_relaxed(reg);
        ddr_type = (val & BM_MMDC_MDMISC_DDR_TYPE) >>
                 BP_MMDC_MDMISC_DDR_TYPE;

        printk(KERN_CRIT "%s MMDC_MDMISC: 0x%08x\n", __func__, val);
        reg = mmdc_base + MMDC_MAPSR;
        /* Enable automatic power saving */
        val = readl_relaxed(reg);
        printk(KERN_CRIT "%s MMDC_MAPSR: 0x%08x\n", __func__, val);
        val &= ~(1 << BP_MMDC_MAPSR_PSD);
        writel_relaxed(val, reg);

        /* Ensure it's successfully enabled */
        while (!(readl_relaxed(reg) & 1 << BP_MMDC_MAPSR_PSS) && --timeout)
                cpu_relax();
<snip>

Any help on the before mentioned issue will be welcomed.

On Wed, Aug 17, 2016 at 8:31 AM, Zhengyu Shen <zhengyu.shen at nxp.com> wrote:
>> The following series of patch resolve the kernel compilation errors with the
>> proposed perf functionality integration into MMDC driver by Zhengyu Shen.
>> These provide the working code which can be enhanced upon as per the
>> reviews from Mark and Peter but will make sure that code compiles without
>> errors and still retains working as was proposed by Zhengyu. I suggest further
>> improvements from review comments could be done on top of it from
>> further on with this being used as a base.
>>
>> Nitin Chaudhary (2):
>>   Error: Fix mmdc compilation errors due to cpu notifier
>>   [i.MX6Q] Code cleanup & verification after fixing compilation error
>>
>>  arch/arm/mach-imx/mmdc.c   | 95 ++++++++++++++++++++++++------------
>> ----------
>>  include/linux/cpuhotplug.h |  1 +
>>  2 files changed, 50 insertions(+), 46 deletions(-)
>>
>> --
>> 2.7.4
>
> Hi, thanks for the help. Is it impossible for two pmus to be created? I wasn't sure
> about that, which is why I didn't have pmu_mmdc set to static.



-- 
Thanks & Regards

Nitin Chaudhary
Nitin Chaudhary
MS, Electrical Engineering
University of Southern California
Intern, Zodiac In-flight Innovations