linux-kernel - Re: [PATCH RFC 2/4] coresight: tmc: set read pointer before dump RAM

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Message-ID: <CAAfSe-vtq6TYaemE5R9H-80uVQ+4eVkKQp3Jom+RvXjFG2r-vQ@mail.gmail.com>
Date:   Tue, 11 Apr 2017 19:25:30 +0800
From:   Chunyan Zhang <zhang.lyra@...il.com>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mike Leach <mike.leach@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>
Subject: Re: [PATCH RFC 2/4] coresight: tmc: set read pointer before dump RAM

On 11 April 2017 at 17:10, Leo Yan <leo.yan@...aro.org> wrote:
> When dump RAM, we need set read pointer so can make sure every time read
> the consistent content. If the RAM is full by checking status register
> (STS), so set the read pointer to same value with write pointer,
> otherwise set read point to 0 so can read from the start of RAM.
>
> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Cc: Mike Leach <mike.leach@...aro.org>
> Cc: Suzuki K Poulose <suzuki.poulose@....com>
> Signed-off-by: Leo Yan <leo.yan@...aro.org>
> ---
>  drivers/hwtracing/coresight/coresight-tmc-etf.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
>
> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c b/drivers/hwtracing/coresight/coresight-tmc-etf.c
> index 6150dac..43cfeaa 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-etf.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c
> @@ -43,10 +43,28 @@ static void tmc_etb_enable_hw(struct tmc_drvdata *drvdata)
>
>  static void tmc_etb_dump_hw(struct tmc_drvdata *drvdata)
>  {
> +       u32 write_ptr, status;
>         char *bufp;
>         u32 read_data;
>         int i;
>
> +       write_ptr = readl_relaxed(drvdata->base + TMC_RWP);

Since 'write_ptr' is only used in the below 'if' branch, I would
suggest to move this statement into that.

Regards,
Chunyan

> +
> +       /*
> +        * Get a hold of the status register and see if a wrap around
> +        * has occurred.  If so adjust things accordingly.
> +        */
> +       status = readl_relaxed(drvdata->base + TMC_STS);
> +       if (status & TMC_STS_FULL)
> +               /* Tell the HW the reading start point */
> +               writel_relaxed(write_ptr, drvdata->base + TMC_RRP);
> +       else
> +               /*
> +                * In case this is not first time to read ETB RAM,
> +                * always write 0 for reading pointer.
> +                */
> +               writel_relaxed(0x0, drvdata->base + TMC_RRP);
> +
>         bufp = drvdata->buf;
>         drvdata->len = 0;
>         while (1) {
> --
> 2.7.4
>