linux-kernel - Re: [PATCHv3 3/4] coresight: etm4x: Add support to enable ETMv4.2

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Date:   Mon, 21 Jan 2019 11:48:31 -0700
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Vivek Gautam <vivek.gautam@...eaurora.org>
Cc:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Rob Herring <robh+dt@...nel.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Leo Yan <leo.yan@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andy Gross <andy.gross@...aro.org>,
        David Brown <david.brown@...aro.org>,
        Doug Anderson <dianders@...omium.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        devicetree@...r.kernel.org, Mark Rutland <mark.rutland@....com>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Sibi Sankar <sibis@...eaurora.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCHv3 3/4] coresight: etm4x: Add support to enable ETMv4.2

On Mon, Jan 21, 2019 at 04:18:36PM +0530, Vivek Gautam wrote:
> 
> On 1/18/2019 5:52 PM, Sai Prakash Ranjan wrote:
> > SDM845 has ETMv4.2 and can use the existing etm4x driver.
> > But the current etm driver checks only for ETMv4.0 and
> > errors out for other etm4x versions. This patch adds this
> > missing support to enable SoC's with ETMv4x to use same
> > driver by checking only the ETM architecture major version
> > number.
> > 
> > Without this change, we get below error during etm probe:
> > 
> > / # dmesg | grep etm
> > [    6.660093] coresight-etm4x: probe of 7040000.etm failed with error -22
> > [    6.666902] coresight-etm4x: probe of 7140000.etm failed with error -22
> > [    6.673708] coresight-etm4x: probe of 7240000.etm failed with error -22
> > [    6.680511] coresight-etm4x: probe of 7340000.etm failed with error -22
> > [    6.687313] coresight-etm4x: probe of 7440000.etm failed with error -22
> > [    6.694113] coresight-etm4x: probe of 7540000.etm failed with error -22
> > [    6.700914] coresight-etm4x: probe of 7640000.etm failed with error -22
> > [    6.707717] coresight-etm4x: probe of 7740000.etm failed with error -22
> > 
> > With this change, etm probe is successful:
> > 
> > / # dmesg | grep coresight
> > [    6.659198] coresight-etm4x 7040000.etm: CPU0: ETM v4.2 initialized
> > [    6.665848] coresight-etm4x 7140000.etm: CPU1: ETM v4.2 initialized
> > [    6.672493] coresight-etm4x 7240000.etm: CPU2: ETM v4.2 initialized
> > [    6.679129] coresight-etm4x 7340000.etm: CPU3: ETM v4.2 initialized
> > [    6.685770] coresight-etm4x 7440000.etm: CPU4: ETM v4.2 initialized
> > [    6.692403] coresight-etm4x 7540000.etm: CPU5: ETM v4.2 initialized
> > [    6.699024] coresight-etm4x 7640000.etm: CPU6: ETM v4.2 initialized
> > [    6.705646] coresight-etm4x 7740000.etm: CPU7: ETM v4.2 initialized
> > 
> > Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
> > ---
> >   drivers/hwtracing/coresight/coresight-etm4x.c | 2 +-
> >   drivers/hwtracing/coresight/coresight-etm4x.h | 2 +-
> >   2 files changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/hwtracing/coresight/coresight-etm4x.c b/drivers/hwtracing/coresight/coresight-etm4x.c
> > index 53e2fb6e86f6..93d5f1f3145e 100644
> > --- a/drivers/hwtracing/coresight/coresight-etm4x.c
> > +++ b/drivers/hwtracing/coresight/coresight-etm4x.c
> > @@ -55,7 +55,7 @@ static void etm4_os_unlock(struct etmv4_drvdata *drvdata)
> >   static bool etm4_arch_supported(u8 arch)
> >   {
> > -	switch (arch) {
> > +	switch (arch >> 4) {
> 
> 
> While this looks good, from what it looks like arch is a combination of
> major version
> minor version. So, will it be better to masks, and shifts macros instead of
> a magic
> number shift.
> But, frankly it's upto Mathieu to decide the readability of this. So, I
> leave it to him.

The layout of the architecture is already well defined in etm4_init_arch_data()
[1].  As such just doing the following would be fine with me:

        /* Mask out the minor version nuber */
        switch (arch & 0xf) {

Of course by proceeding this way we don't need to modify the define in
coresight-etm4x.h.

Regards,
Mathieu

[1]. https://elixir.bootlin.com/linux/latest/source/drivers/hwtracing/coresight/coresight-etm4x.c#L508

> 
> Thanks
> Vivek
> 
> >   	case ETM_ARCH_V4:
> >   		break;
> >   	default:
> > diff --git a/drivers/hwtracing/coresight/coresight-etm4x.h b/drivers/hwtracing/coresight/coresight-etm4x.h
> > index 52786e9d8926..05d4bd330881 100644
> > --- a/drivers/hwtracing/coresight/coresight-etm4x.h
> > +++ b/drivers/hwtracing/coresight/coresight-etm4x.h
> > @@ -136,7 +136,7 @@
> >   #define ETM_MAX_RES_SEL			16
> >   #define ETM_MAX_SS_CMP			8
> > -#define ETM_ARCH_V4			0x40
> > +#define ETM_ARCH_V4			0x4
> >   #define ETMv4_SYNC_MASK			0x1F
> >   #define ETM_CYC_THRESHOLD_MASK		0xFFF
> >   #define ETM_CYC_THRESHOLD_DEFAULT       0x100