linux-kernel - Re: [PATCH v4 1/3] bus: mhi: core: Introduce internal register poll helper function

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Date:   Thu, 11 Mar 2021 09:00:36 +0100
From:   Loic Poulain <loic.poulain@...aro.org>
To:     Bhaumik Bhatt <bbhatt@...eaurora.org>
Cc:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Hemant Kumar <hemantk@...eaurora.org>,
        Jeffrey Hugo <jhugo@...eaurora.org>,
        open list <linux-kernel@...r.kernel.org>,
        Carl Yin(殷张成) <carl.yin@...ctel.com>,
        Naveen Kumar <naveen.kumar@...ctel.com>
Subject: Re: [PATCH v4 1/3] bus: mhi: core: Introduce internal register poll
 helper function

Hi Bhaumik,

On Thu, 11 Mar 2021 at 00:31, Bhaumik Bhatt <bbhatt@...eaurora.org> wrote:
>
> Introduce helper function to allow MHI core driver to poll for
> a value in a register field. This helps reach a common path to
> read and poll register values along with a retry time interval.
>
> Signed-off-by: Bhaumik Bhatt <bbhatt@...eaurora.org>
> ---
>  drivers/bus/mhi/core/internal.h |  3 +++
>  drivers/bus/mhi/core/main.c     | 23 +++++++++++++++++++++++
>  2 files changed, 26 insertions(+)
>
> diff --git a/drivers/bus/mhi/core/internal.h b/drivers/bus/mhi/core/internal.h
> index 6f80ec3..005286b 100644
> --- a/drivers/bus/mhi/core/internal.h
> +++ b/drivers/bus/mhi/core/internal.h
> @@ -643,6 +643,9 @@ int __must_check mhi_read_reg(struct mhi_controller *mhi_cntrl,
>  int __must_check mhi_read_reg_field(struct mhi_controller *mhi_cntrl,
>                                     void __iomem *base, u32 offset, u32 mask,
>                                     u32 shift, u32 *out);
> +int __must_check mhi_poll_reg_field(struct mhi_controller *mhi_cntrl,
> +                                   void __iomem *base, u32 offset, u32 mask,
> +                                   u32 shift, u32 val, u32 delayus);
>  void mhi_write_reg(struct mhi_controller *mhi_cntrl, void __iomem *base,
>                    u32 offset, u32 val);
>  void mhi_write_reg_field(struct mhi_controller *mhi_cntrl, void __iomem *base,
> diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
> index 4e0131b..7c7f41a 100644
> --- a/drivers/bus/mhi/core/main.c
> +++ b/drivers/bus/mhi/core/main.c
> @@ -4,6 +4,7 @@
>   *
>   */
>
> +#include <linux/delay.h>
>  #include <linux/device.h>
>  #include <linux/dma-direction.h>
>  #include <linux/dma-mapping.h>
> @@ -37,6 +38,28 @@ int __must_check mhi_read_reg_field(struct mhi_controller *mhi_cntrl,
>         return 0;
>  }
>
> +int __must_check mhi_poll_reg_field(struct mhi_controller *mhi_cntrl,
> +                                   void __iomem *base, u32 offset,
> +                                   u32 mask, u32 shift, u32 val, u32 delayus)
> +{
> +       int ret;
> +       u32 out, retry = (mhi_cntrl->timeout_ms * 1000) / delayus;
> +
> +       while (retry--) {
> +               ret = mhi_read_reg_field(mhi_cntrl, base, offset, mask, shift,
> +                                        &out);
> +               if (ret)
> +                       return ret;
> +
> +               if (out == val)
> +                       return 0;
> +
> +               udelay(delayus);

Have you read my previous comment?
Do you really want to risk hogging the CPU for several seconds? we
know that some devices take several seconds to start/boot.
Why not using msleep variant here?

Regards,
Loic