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From: Samuel Holland <samuel@sholland.org>
To: "Wolfram Sang" <wsa@kernel.org>, "Marek Behún" <kabel@kernel.org>,
	"Gregory CLEMENT" <gregory.clement@bootlin.com>,
	linux-i2c@vger.kernel.org, "Ondrej Jirman" <megous@megous.com>
Subject: Re: [PATCH] i2c: mv64xxx: Fix random system lock caused by runtime PM
Date: Wed, 14 Apr 2021 08:42:11 -0500
Message-ID: <01f2a007-39d8-d7c0-b3bc-ef379956d43e@sholland.org> (raw)
In-Reply-To: <20210413195854.GB2751@kunai>

On 4/13/21 2:58 PM, Wolfram Sang wrote:
> On Thu, Apr 08, 2021 at 04:00:00AM +0200, Marek Behún wrote:
>> I noticed a weird bug with this driver on Marvell CN9130 Customer
>> Reference Board.
>>
>> Sometime after boot, the system locks with the following message:
>>  [104.071363] i2c i2c-0: mv64xxx: I2C bus locked, block: 1, time_left: 0
>>
>> The system does not respond afterwards, only warns about RCU stalls.
>>
>> This first appeared with commit e5c02cf54154 ("i2c: mv64xxx: Add runtime
>> PM support").
>>
>> With further experimentation I discovered that adding a delay into
>> mv64xxx_i2c_hw_init() fixes this issue. This function is called before
>> every xfer, due to how runtime PM works in this driver. It seems that in
>> order to work correctly, a delay is needed after the bus is reset in
>> this function.
>>
>> Since there already is a known erratum with this controller needing a
>> delay, I assume that this is just another place this needs to be
>> applied. Therefore I apply the delay only if errata_delay is true.
>>
>> Signed-off-by: Marek Behún <kabel@kernel.org>
> 
> Gregory? Looks reasonable to me and if so, we should have this in 5.12
> already. Comments from others are welcome, too, of course.

I also don't have an affected platform, so I did not notice this when adding
runtime PM. The change makes sense to me as well.

Reviewed-by: Samuel Holland <samuel@sholland.org>

Cheers,
Samuel

>> ---
>>  drivers/i2c/busses/i2c-mv64xxx.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/i2c/busses/i2c-mv64xxx.c b/drivers/i2c/busses/i2c-mv64xxx.c
>> index c590d36b5fd1..5c8e94b6cdb5 100644
>> --- a/drivers/i2c/busses/i2c-mv64xxx.c
>> +++ b/drivers/i2c/busses/i2c-mv64xxx.c
>> @@ -221,6 +221,10 @@ mv64xxx_i2c_hw_init(struct mv64xxx_i2c_data *drv_data)
>>  	writel(0, drv_data->reg_base + drv_data->reg_offsets.ext_addr);
>>  	writel(MV64XXX_I2C_REG_CONTROL_TWSIEN | MV64XXX_I2C_REG_CONTROL_STOP,
>>  		drv_data->reg_base + drv_data->reg_offsets.control);
>> +
>> +	if (drv_data->errata_delay)
>> +		udelay(5);
>> +
>>  	drv_data->state = MV64XXX_I2C_STATE_IDLE;
>>  }
>>  
>> -- 
>> 2.26.2
>>


  parent reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-08  2:00 Marek Behún
2021-04-10 16:47 ` Marek Behún
2021-04-13 19:58 ` Wolfram Sang
2021-04-14 13:28   ` Gregory CLEMENT
2021-04-14 14:29     ` Marek Behún
2021-04-14 13:42   ` Samuel Holland [this message]
2021-04-15 20:13 ` Wolfram Sang

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