From: Jonathan Liu <net147@gmail.com>
To: Chen-Yu Tsai <wens@csie.org>,
Maxime Ripard <maxime.ripard@free-electrons.com>
Cc: David Airlie <airlied@linux.ie>,
linux-kernel <linux-kernel@vger.kernel.org>,
dri-devel <dri-devel@lists.freedesktop.org>,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
linux-sunxi <linux-sunxi@googlegroups.com>
Subject: Re: [PATCH v5] drm/sun4i: hdmi: Implement I2C adapter for A10s DDC bus
Date: Sat, 1 Jul 2017 00:14:44 +1000 [thread overview]
Message-ID: <CANwerB2RHQwZgZc37+dkh9np-SSFks3tZxqFzDPVwQP5oP48hg@mail.gmail.com> (raw)
In-Reply-To: <CAGb2v67CTXayDm4rhoJ4CNx9J=u+U+2_kh9xYsjHjCE8YnJ=ow@mail.gmail.com>
Hi Chen-Yu and Maxime,
On 30 June 2017 at 13:16, Chen-Yu Tsai <wens@csie.org> wrote:
> On Fri, Jun 30, 2017 at 6:22 AM, Jonathan Liu <net147@gmail.com> wrote:
>> Hi Maxime,
>>
>> On 30 June 2017 at 01:56, Maxime Ripard
>> <maxime.ripard@free-electrons.com> wrote:
>>> 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?
>>>
>>
>> When an error occurs one of the error bits will be set in the
>> INT_STATUS register so this is detected very quickly if I check the
>> INT_STATUS and FIFO_STATUS at the same time. The 100 ms timeout is in
>> case the I2C slave does clock stretching in which case the transfer
>> may take longer than the predicted time.
>>
>>> 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.
>>>
>>
>> I did try that when I was doing the v3 patch but I couldn't get it to
>> work as mentioned previously in the v3 patch discussion. I programmed
>> the FIFO_RX_TRIGGER_THRES and FIFO_TX_TRIGGER_THRES in DDC_FIFO_Ctrl
>> register at the same time as setting FIFO_Address_Clear but the
>> request interrupt status bit did not get updated to the appropriate
>> state that is consistent with the FIFO level and the thresholds. I did
>> try this several times for subsequent patch versions without success.
>
> The manual says "When FIFO level is above this value in read mode, DMA
> request and FIFO request interrupt are asserted if relative enable is on."
>
> Perhaps try enabling the interrupts? But if that were the case, wouldn't
> using interrupts instead of polling be better?
>
> ChenYu
>
I managed to get the thresholds working so switching to using
interrupts instead of polling will be my next goal.
>>
>>> Maxime
>>>
>>> --
>>> Maxime Ripard, Free Electrons
>>> Embedded Linux and Kernel engineering
>>> http://free-electrons.com
>>
>> Regards,
>> Jonathan
Regards,
Jonathan
next prev parent reply other threads:[~2017-06-30 14:14 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-27 14:36 [PATCH v5] drm/sun4i: hdmi: Implement I2C adapter for A10s DDC bus Jonathan Liu
2017-06-28 9:20 ` Maxime Ripard
2017-06-28 10:39 ` Jonathan Liu
2017-06-29 15:56 ` Maxime Ripard
2017-06-29 22:22 ` Jonathan Liu
2017-06-30 3:16 ` Chen-Yu Tsai
2017-06-30 14:14 ` Jonathan Liu [this message]
2017-06-30 16:01 ` Maxime Ripard
2017-06-30 9:34 ` Maxime Ripard
2017-06-30 9:58 ` Jonathan Liu
2017-07-01 6:29 ` Jonathan Liu
2017-06-28 22:06 ` kbuild test robot
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