Re: [PATCH v2] i2c: piix4: Avoid race conditions with IMC

[Andy Shevchenko <andy.shevchenko@gmail.com>]

On Wed, Jan 11, 2017 at 11:11 AM, Ricardo Ribalda Delgado
<ricardo.ribalda@gmail.com> wrote:
> On AMD's SB800 and upwards, the SMBus is shared with the Integrated
> Micro Controller (IMC).
>
> The platform provides a hardware semaphore to avoid race conditions
> among them. (Check page 288 of the SB800-Series Southbridges Register
> Reference Guide http://support.amd.com/TechDocs/45482.pdf)
>
> Without this patch, many access to the SMBus end with an invalid
> transaction or even with the bus stalled.
>

After addressing below comment
FWIW: Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>:

> Credit-to: Alexandre Desnoyers <alex@qtec.com>

It would be nice to put in plain test what you tell in the discussion
here instead of non-standard (see submitting-patches.rst) tag.

> Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
> ---
>
> v2: Suggestions by Andy Shevchenko <andy.shevchenko@gmail.com>:
>  -Rename timeout to retries
>  -Use do {} while(--retries) pattern
>  -Group new variables
>
>
>  drivers/i2c/busses/i2c-piix4.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
>
> diff --git a/drivers/i2c/busses/i2c-piix4.c b/drivers/i2c/busses/i2c-piix4.c
> index f0563f7ce01b..81d06be0a72d 100644
> --- a/drivers/i2c/busses/i2c-piix4.c
> +++ b/drivers/i2c/busses/i2c-piix4.c
> @@ -585,10 +585,29 @@ static s32 piix4_access_sb800(struct i2c_adapter *adap, u16 addr,
>                  u8 command, int size, union i2c_smbus_data *data)
>  {
>         struct i2c_piix4_adapdata *adapdata = i2c_get_adapdata(adap);
> +       unsigned short piix4_smba = adapdata->smba;
> +       int retries = MAX_TIMEOUT;
> +       int smbslvcnt;
>         u8 smba_en_lo;
>         u8 port;
>         int retval;
>
> +       /* Request the SMBUS semaphore, avoid conflicts with the IMC */
> +       smbslvcnt  = inb_p(SMBSLVCNT);
> +       do {
> +               outb_p(smbslvcnt | 0x10, SMBSLVCNT);
> +
> +               /* Check the semaphore status */
> +               smbslvcnt  = inb_p(SMBSLVCNT);
> +               if (smbslvcnt & 0x10)
> +                       break;
> +
> +               usleep_range(1000, 2000);
> +       } while (--retries);
> +       /* SMBus is still owned by the IMC, we give up */
> +       if (!retries)
> +               return -EBUSY;
> +
>         mutex_lock(&piix4_mutex_sb800);
>
>         outb_p(piix4_port_sel_sb800, SB800_PIIX4_SMB_IDX);
> @@ -606,6 +625,9 @@ static s32 piix4_access_sb800(struct i2c_adapter *adap, u16 addr,
>
>         mutex_unlock(&piix4_mutex_sb800);
>
> +       /* Release the semaphore */
> +       outb_p(smbslvcnt | 0x20, SMBSLVCNT);
> +
>         return retval;
>  }
>
> --
> 2.11.0
>



-- 
With Best Regards,
Andy Shevchenko