On Tue, Jan 10, 2017 at 2:16 PM, Ricardo Ribalda Delgado <ricardo.ribalda@xxxxxxxxx> 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) It would be nice to understand what kind of devices are accessing and to where. Hans seems discovered one pretty nice issue on Intel BayTrail/CherryTrail platforms where I2C semaphore is used to prevent simultaneous access to P-Unit, but we have two paths there which are not synchronized (yet). It brings a set of interesting (and unfortunately "famous") bugs. > > Without this patch, many access to the SMBus end with an invalid > transaction or even with the bus stalled. > > Credit-to: Alexandre Desnoyers <alex@xxxxxxxx> Never saw before. Did he suggested the solution or what? > --- a/drivers/i2c/busses/i2c-piix4.c > +++ b/drivers/i2c/busses/i2c-piix4.c > @@ -585,9 +585,28 @@ 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; > u8 smba_en_lo; > u8 port; > int retval; > + int timeout = 0; > + int smbslvcnt; Keep them just after your another added variable. > + /* Request the SMBUS semaphore, avoid conflicts with the IMC */ > + smbslvcnt = inb_p(SMBSLVCNT); > + while (++timeout < MAX_TIMEOUT) { Usual pattern is countdown. do { ... } while (--timeout); > + outb_p(smbslvcnt | 0x10, SMBSLVCNT); > + > + /* Check the semaphore status */ > + smbslvcnt = inb_p(SMBSLVCNT); > + if (smbslvcnt & 0x10) > + break; > + > + usleep_range(1000, 2000); > + } > + /* SMBus is still owned by the IMC, we give up */ > + if (timeout == MAX_TIMEOUT) > + return -EBUSY; Would caller do it again? Perhaps -EAGAIN? Since the returned value is not -ETIMEDOUT, I suppose the name of counter variable is a bit confusing. Basically it's amount of attempts with some gap between them. Though, it's up to you and maintainer. > + /* Release the semaphore */ > + outb_p(smbslvcnt | 0x20, SMBSLVCNT); -- With Best Regards, Andy Shevchenko -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
