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

From: Akash Asthana
Date: Mon Jul 27 2020 - 04:36:52 EST

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

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:

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

I have posted a patch to update maintainers list. Patch: [MAINTAINERS: Update Geni I2C maintainers list]

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



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