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Subject: Re: [PATCH v2] i2c: i2c-qcom-geni: Fix DMA transfer race
To:     Stephen Boyd <swboyd@chromium.org>,
        Douglas Anderson <dianders@chromium.org>,
        Wolfram Sang <wsa@the-dreams.de>
Cc:     Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>,
        Akash Asthana <akashast@codeaurora.org>,
        Rajendra Nayak <rnayak@codeaurora.org>,
        Alok Chauhan <alokc@codeaurora.org>,
        Andy Gross <agross@kernel.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Girish Mahadevan <girishm@codeaurora.org>,
        Karthikeyan Ramasubramanian <kramasub@codeaurora.org>,
        Sagar Dharia <sdharia@codeaurora.org>,
        linux-arm-msm@vger.kernel.org, linux-i2c@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20200722145948.v2.1.I7efdf6efaa6edadbb690196cd4fbe3392a582c89@changeid>
 <159546541191.3847286.3212989047313785097@swboyd.mtv.corp.google.com>
From:   "Mukesh, Savaliya" <msavaliy@codeaurora.org>
Message-ID: <bb8b1e99-2f55-910c-c37f-5e0fef0fb4b1@codeaurora.org>
Date:   Thu, 23 Jul 2020 11:46:28 +0530
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On 7/23/2020 6:20 AM, Stephen Boyd wrote:
> Quoting Douglas Anderson (2020-07-22 15:00:21)
>> When I have KASAN enabled on my kernel and I start stressing the
>> touchscreen my system tends to hang.  The touchscreen is one of the
>> only things that does a lot of big i2c transfers and ends up hitting
>> the DMA paths in the geni i2c driver.  It appears that KASAN adds
>> enough delay in my system to tickle a race condition in the DMA setup
>> code.
>>
>> When the system hangs, I found that it was running the geni_i2c_irq()
>> over and over again.  It had these:
>>
>> m_stat   = 0x04000080
>> rx_st    = 0x30000011
>> dm_tx_st = 0x00000000
>> dm_rx_st = 0x00000000
>> dma      = 0x00000001
>>
>> Notably we're in DMA mode but are getting M_RX_IRQ_EN and
>> M_RX_FIFO_WATERMARK_EN over and over again.
>>
>> Putting some traces in geni_i2c_rx_one_msg() showed that when we
>> failed we were getting to the start of geni_i2c_rx_one_msg() but were
>> never executing geni_se_rx_dma_prep().
>>
>> I believe that the problem here is that we are starting the geni
>> command before we run geni_se_rx_dma_prep().  If a transfer makes it
>> far enough before we do that then we get into the state I have
>> observed.  Let's change the order, which seems to work fine.
>>
>> Although problems were seen on the RX path, code inspection suggests
>> that the TX should be changed too.  Change it as well.
>>
>> Fixes: 37692de5d523 ("i2c: i2c-qcom-geni: Add bus driver for the Qualcomm GENI I2C controller")
>> Signed-off-by: Douglas Anderson <dianders@chromium.org>
>> Tested-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
>> Reviewed-by: Akash Asthana <akashast@codeaurora.org>
Reviewed-by: Mukesh Kumar Savaliya <msavaliy@codeaurora.org>
>> ---
> Reviewed-by: Stephen Boyd <swboyd@chromium.org>