linux-kernel - Re: [PATCH -next] i2c: designware: Fix improper usage of readl

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Message-ID: <YhZNu0pHKiK9Vf55@smile.fi.intel.com>
Date:   Wed, 23 Feb 2022 17:07:39 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Jan Dabros <jsd@...ihalf.com>
Cc:     linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
        jarkko.nikula@...ux.intel.com, wsa@...nel.org,
        rrangel@...omium.org, upstream@...ihalf.com,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH -next] i2c: designware: Fix improper usage of readl

On Fri, Feb 18, 2022 at 02:33:48PM +0100, Jan Dabros wrote:
> Kernel test robot reported incorrect type in argument 1 of readl(), but
> more importantly it brought attention that MMIO accessor shouldn't be
> used in this case, since req->hdr.status is part of a command-response
> buffer in system memory.
> 
> Since its value may be altered by PSP outside of the scope of current
> thread (somehow similar to IRQ handler case), we need to use
> READ_ONCE() to ensure compiler won't optimize this call.
> 
> Fix also 'status' variable type to reflect that corresponding field in
> command-response buffer is platform-independent u32.

Thanks for the fix, seems reasonable to me.
Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

> Signed-off-by: Jan Dabros <jsd@...ihalf.com>
> Reported-by: kernel test robot <lkp@...el.com>
> ---
>  drivers/i2c/busses/i2c-designware-amdpsp.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-designware-amdpsp.c b/drivers/i2c/busses/i2c-designware-amdpsp.c
> index 752e0024db03..c64e459afb5c 100644
> --- a/drivers/i2c/busses/i2c-designware-amdpsp.c
> +++ b/drivers/i2c/busses/i2c-designware-amdpsp.c
> @@ -160,9 +160,10 @@ static int psp_send_cmd(struct psp_i2c_req *req)
>  /* Helper to verify status returned by PSP */
>  static int check_i2c_req_sts(struct psp_i2c_req *req)
>  {
> -	int status;
> +	u32 status;
>  
> -	status = readl(&req->hdr.status);
> +	/* Status field in command-response buffer is updated by PSP */
> +	status = READ_ONCE(req->hdr.status);
>  
>  	switch (status) {
>  	case PSP_I2C_REQ_STS_OK:
> -- 
> 2.35.1.265.g69c8d7142f-goog
> 

-- 
With Best Regards,
Andy Shevchenko