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Re: [PATCH v5] drm/sun4i: hdmi: Implement I2C adapter for A10s DDC bus

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On Wed, Jun 28, 2017 at 08:39:33PM +1000, Jonathan Liu wrote:
> >> +     u32 int_status;
> >> +     u32 fifo_status;
> >> +     /* Read needs empty flag unset, write needs full flag unset */
> >> +     u32 flag = read ? SUN4I_HDMI_DDC_FIFO_STATUS_EMPTY :
> >> +                       SUN4I_HDMI_DDC_FIFO_STATUS_FULL;
> >> +     int ret;
> >> +
> >> +     /* Wait until error or FIFO ready */
> >> +     ret = readl_poll_timeout(hdmi->base + SUN4I_HDMI_DDC_INT_STATUS_REG,
> >> +                              int_status,
> >> +                              is_err_status(int_status) ||
> >> +                              is_fifo_flag_unset(hdmi, &fifo_status, flag),
> >> +                              min(len, SUN4I_HDMI_DDC_FIFO_SIZE) * byte_time,
> >> +                              100000);
> >> +
> >> +     if (is_err_status(int_status))
> >> +             return -EIO;
> >> +     if (ret)
> >> +             return -ETIMEDOUT;
> >
> > Why not just have
> > ret = readl_poll_timeout(hdmi->base + SUN4I_HDMI_DDC_FIFO_STATUS_REG, reg,
> >                          !(reg & flag), 100, 100000);
> >
> > if (ret < 0)
> >         if (is_err_status())
> >                 return -EIO;
> >         return ret;
> >
> >
> 
> If I check error status after readl_poll_timeout and there is an error
> (e.g. the I2C address does not have a corresponding device connected
> or nothing connected to HDMI port) it will keep checking the fifo
> status even though error bit is set in the int status and then timeout
> after 100 ms. If it checks the int status register at the same time,
> it will error after 100 nanoseconds. I don't want to introduce
> unnecessary delays considering part of the reason for adding this
> driver to make it more usable for non-standard use cases.

Well, polling for 100ms doesn't seem great either. What was the
rationale behind that timeout?

And we can also reverse the check and look at the INT_STATUS
register. The errors will be there, and we can program the threshold
we want in both directions and use the
DDC_FIFO_Request_Interrupt_Status bit.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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[PATCH v5] drm/sun4i: hdmi: Implement I2C adapter for A10s DDC bus Jonathan Liu <net147@gmail.com> - 2017-06-27 16:40 +0200
  Re: [PATCH v5] drm/sun4i: hdmi: Implement I2C adapter for A10s DDC  bus Maxime Ripard <maxime.ripard@free-electrons.com> - 2017-06-28 11:30 +0200
    Re: [PATCH v5] drm/sun4i: hdmi: Implement I2C adapter for A10s DDC bus Jonathan Liu <net147@gmail.com> - 2017-06-28 12:50 +0200
      Re: [PATCH v5] drm/sun4i: hdmi: Implement I2C adapter for A10s DDC  bus Maxime Ripard <maxime.ripard@free-electrons.com> - 2017-06-29 18:00 +0200
        Re: [PATCH v5] drm/sun4i: hdmi: Implement I2C adapter for A10s DDC bus Jonathan Liu <net147@gmail.com> - 2017-06-30 00:30 +0200
          Re: [PATCH v5] drm/sun4i: hdmi: Implement I2C adapter for A10s DDC bus Chen-Yu Tsai <wens@csie.org> - 2017-06-30 05:20 +0200
            Re: [PATCH v5] drm/sun4i: hdmi: Implement I2C adapter for A10s DDC bus Jonathan Liu <net147@gmail.com> - 2017-06-30 16:20 +0200
              Re: [PATCH v5] drm/sun4i: hdmi: Implement I2C adapter for A10s DDC  bus Maxime Ripard <maxime.ripard@free-electrons.com> - 2017-06-30 18:10 +0200
          Re: [PATCH v5] drm/sun4i: hdmi: Implement I2C adapter for A10s DDC  bus Maxime Ripard <maxime.ripard@free-electrons.com> - 2017-06-30 11:40 +0200
            Re: [PATCH v5] drm/sun4i: hdmi: Implement I2C adapter for A10s DDC bus Jonathan Liu <net147@gmail.com> - 2017-06-30 12:00 +0200
              Re: [PATCH v5] drm/sun4i: hdmi: Implement I2C adapter for A10s DDC bus Jonathan Liu <net147@gmail.com> - 2017-07-01 08:30 +0200
  Re: [PATCH v5] drm/sun4i: hdmi: Implement I2C adapter for A10s DDC  bus kbuild test robot <lkp@intel.com> - 2017-06-29 00:10 +0200

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