linux-kernel - Re: [PATCH 5.10 002/299] bus: mhi: core: Clear configuration from channel context during reset

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Date:   Mon, 10 May 2021 22:56:50 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Bhaumik Bhatt <bbhatt@...eaurora.org>,
        Hemant Kumar <hemantk@...eaurora.org>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Subject: Re: [PATCH 5.10 002/299] bus: mhi: core: Clear configuration from
 channel context during reset

Hi!

> From: Bhaumik Bhatt <bbhatt@...eaurora.org>
> 
> commit 47705c08465931923e2f2b506986ca0bdf80380d upstream.
> 
> When clearing up the channel context after client drivers are
> done using channels, the configuration is currently not being
> reset entirely. Ensure this is done to appropriately handle
> issues where clients unaware of the context state end up calling
> functions which expect a context.

> +++ b/drivers/bus/mhi/core/init.c
> @@ -544,6 +544,7 @@ void mhi_deinit_chan_ctxt(struct mhi_con
> +	u32 tmp;
> @@ -554,7 +555,19 @@ void mhi_deinit_chan_ctxt(struct mhi_con
...
> +	tmp = chan_ctxt->chcfg;
> +	tmp &= ~CHAN_CTX_CHSTATE_MASK;
> +	tmp |= (MHI_CH_STATE_DISABLED << CHAN_CTX_CHSTATE_SHIFT);
> +	chan_ctxt->chcfg = tmp;
> +
> +	/* Update to all cores */
> +	smp_wmb();
>  }

This is really interesting code; author was careful to make sure chcfg
is updated atomically, but C compiler is free to undo that. Plus, this
will make all kinds of checkers angry.

Does the file need to use READ_ONCE and WRITE_ONCE?

Best regards,
								Pavel
-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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