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

[Akash Asthana]

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@xxxxxxxxxxxx>
> > > Tested-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>
> > > Reviewed-by: Akash Asthana <akashast@xxxxxxxxxxxxxx>
> > 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@xxxxxxxxxxxxx/

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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