Re: [PATCH v2] i2c: i2c-qcom-geni: Fix DMA transfer race

From: Akash Asthana <akashast@codeaurora.org>
To: Wolfram Sang <wsa@the-dreams.de>,
	Douglas Anderson <dianders@chromium.org>
Cc: swboyd@chromium.org, msavaliy@codeaurora.org,
	Sai Prakash Ranjan <saiprakash.ranjan@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
Subject: Re: [PATCH v2] i2c: i2c-qcom-geni: Fix DMA transfer race
Date: Mon, 27 Jul 2020 14:06:36 +0530	[thread overview]
Message-ID: <ed066f01-0c3a-a14b-5616-cbdfd074bfeb@codeaurora.org> (raw)
In-Reply-To: <20200726124747.GA16169@ninjato>

On 7/26/2020 6:17 PM, Wolfram Sang wrote:
> On Thu, Jul 23, 2020 at 09:56:34PM +0200, Wolfram Sang wrote:
>> On Wed, Jul 22, 2020 at 03:00:21PM -0700, Douglas Anderson wrote:
>>> 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>
>> Applied to for-current, thanks!
> Glad we got this sorted. I just wondered that Alok wasn't part of the
> discussion. Is he still interested in maintaining the driver? Also
> because there is an unprocessed patch left for this driver:
>
> http://patchwork.ozlabs.org/project/linux-i2c/patch/20191103212204.13606-1-colin.king@canonical.com/

Alok has moved out of GENI team, he no longer supports GENI I2C drivers.

I have posted a patch to update maintainers list. Patch: 
https://patchwork.kernel.org/patch/11686541/ [MAINTAINERS: Update Geni 
I2C maintainers list]

Also, Girish Mahadevan, Sagar Dharia and Karthikeyan Ramasubramanian  no 
longer supports GENI drivers.

Regards,

Akash

>
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