Date:   Thu, 5 Oct 2017 16:22:17 +0200
From:   Jean Delvare <jdelvare@...e.de>
To:     Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
Cc:     Wolfram Sang <wsa@...-dreams.de>, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i2c: piix4: Disable completely the IMC during 
 SMBUS_BLOCK_DATA

Hi Ribalda,

On Thu, 21 Sep 2017 09:37:43 +0200, Ricardo Ribalda Delgado wrote:
> SMBUS_BLOCK_DATA transactions might fail due to a race condition with
> the IMC, even when the IMC semaphore is used.

An explanation of what IMC stands for, both in description and in the
code, would be appreciated.

What are the consequences of disabling the IMC temporarily at random
times?

> This bug has been reported and confirmed by AMD, who suggested as a
> solution an IMC firmware upgrade (obtained via BIOS update) and
> disabling the IMC during SMBUS_BLOCK_DATA transactions.
> 
> Even without the IMC upgrade, the smbus is much more stable with this
> patch.
>
> Tested on a Bettong-alike board.

Unfortunately I no longer have any system with a compatible chipset so
I can't test.

> Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
> ---
>  drivers/i2c/busses/i2c-piix4.c | 89 ++++++++++++++++++++++++++++++++++++++----
>  1 file changed, 82 insertions(+), 7 deletions(-)

First of all: your patch adds the following 2 warnings which you will
have to fix before acceptance:

  CC [M]  drivers/i2c/busses/i2c-piix4.o
drivers/i2c/busses/i2c-piix4.c:591:5: warning: no previous prototype for ‘piix4_imc_sleep’ [-Wmissing-prototypes]
 int piix4_imc_sleep(void)
     ^
drivers/i2c/busses/i2c-piix4.c:608:6: warning: no previous prototype for ‘piix4_imc_wakeup’ [-Wmissing-prototypes]
 void piix4_imc_wakeup(void)
      ^

As far as I can see these functions should be static.

> diff --git a/drivers/i2c/busses/i2c-piix4.c b/drivers/i2c/busses/i2c-piix4.c
> index 0ecdb47a23ab..3b8a5eaad956 100644
> --- a/drivers/i2c/busses/i2c-piix4.c
> +++ b/drivers/i2c/busses/i2c-piix4.c
> @@ -85,6 +85,8 @@
>  /* SB800 constants */
>  #define SB800_PIIX4_SMB_IDX		0xcd6
>  
> +#define IMC_SMB_IDX			0x3e
> +
>  /*
>   * SB800 port is selected by bits 2:1 of the smb_en register (0x2c)
>   * or the smb_sel register (0x2e), depending on bit 0 of register 0x2f.
> @@ -160,6 +162,8 @@ struct i2c_piix4_adapdata {
>  	/* SB800 */
>  	bool sb800_main;
>  	u8 port;		/* Port number, shifted */
> +
> +	bool notify_imc;

Put right after sb800_main?

>  };
>  
>  static int piix4_setup(struct pci_dev *PIIX4_dev,
> @@ -572,6 +576,50 @@ static s32 piix4_access(struct i2c_adapter * adap, u16 addr,
>  	return 0;
>  }
>  
> +static uint8_t piix4_imc_read(uint8_t idx)
> +{
> +	outb_p(idx, IMC_SMB_IDX);
> +	return inb_p(IMC_SMB_IDX + 1);

Please define IMC_SMB_DAT or some such, and use it.

> +}
> +
> +static void piix4_imc_write(uint8_t idx, uint8_t value)
> +{
> +	outb_p(idx, IMC_SMB_IDX);
> +	outb_p(value, IMC_SMB_IDX + 1);
> +}
> +
> +int piix4_imc_sleep(void)
> +{
> +	int timeout = MAX_TIMEOUT;
> +
> +	piix4_imc_write(0x82, 0x00);
> +	piix4_imc_write(0x83, 0xB4);
> +	piix4_imc_write(0x80, 0x96);
> +
> +	while (timeout--) {
> +		if (piix4_imc_read(0x82) == 0xfa)
> +			return 0;
> +		usleep_range(1000, 2000);
> +	}

Is there some minimum time we know we'll have to wait before completion?

> +
> +	return -ETIMEDOUT;
> +}
> +
> +void piix4_imc_wakeup(void)
> +{
> +	int timeout = MAX_TIMEOUT;
> +
> +	piix4_imc_write(0x82, 0x00);
> +	piix4_imc_write(0x83, 0xB5);
> +	piix4_imc_write(0x80, 0x96);
> +
> +	while (timeout--) {
> +		if (piix4_imc_read(0x82) == 0xfa)
> +			break;
> +		usleep_range(1000, 2000);
> +	}

Same question here.

Why don't you check for timeout here?

In both functions above, you will write the same value to IMC_SMB_IDX
again and again while checking for completion. Is this a hardware
requirement? If not, it would be more efficient to implement some
piix4_imc_quick_read() function which assumes that the index is already
set.

> +}
> +
>  /*
>   * Handles access to multiple SMBus ports on the SB800.
>   * The port is selected by bits 2:1 of the smb_en register (0x2c).
> @@ -586,7 +634,7 @@ static s32 piix4_access_sb800(struct i2c_adapter *adap, u16 addr,
>  {
>  	struct i2c_piix4_adapdata *adapdata = i2c_get_adapdata(adap);
>  	unsigned short piix4_smba = adapdata->smba;
> -	int retries = MAX_TIMEOUT;
> +	int retries = adapdata->notify_imc ? MAX_TIMEOUT * 2 : MAX_TIMEOUT;

What's the rationale for this change?

>  	int smbslvcnt;
>  	u8 smba_en_lo;
>  	u8 port;
> @@ -612,6 +660,15 @@ static s32 piix4_access_sb800(struct i2c_adapter *adap, u16 addr,
>  		return -EBUSY;
>  	}
>  
> +	/* Block data transfers require disabling the imc */

IMC in capitals please. And they *may* require - not all chipsets are
affected.

> +	if ((size == I2C_SMBUS_BLOCK_DATA) && adapdata->notify_imc)
> +		/* If IMC communication fails do not retry*/
> +		if (piix4_imc_sleep()) {
> +			dev_warn(&adap->dev,
> +				 "Failed to communicate with the IMC, enable it and/or upgrade your BIOS.\n");

The IMC is a hardware thing, how is upgrading the BIOS supposed to
help? Is there no way to check if the IMC is actually disabled, to
print a more accurate message?

> +			adapdata->notify_imc = false;
> +		}
> +
>  	outb_p(piix4_port_sel_sb800, SB800_PIIX4_SMB_IDX);
>  	smba_en_lo = inb_p(SB800_PIIX4_SMB_IDX + 1);
>  
> @@ -628,6 +685,9 @@ static s32 piix4_access_sb800(struct i2c_adapter *adap, u16 addr,
>  	/* Release the semaphore */
>  	outb_p(smbslvcnt | 0x20, SMBSLVCNT);
>  
> +	if ((size == I2C_SMBUS_BLOCK_DATA) && adapdata->notify_imc)
> +		piix4_imc_wakeup();
> +
>  	mutex_unlock(&piix4_mutex_sb800);
>  
>  	return retval;
> @@ -679,7 +739,7 @@ static struct i2c_adapter *piix4_main_adapters[PIIX4_MAX_ADAPTERS];
>  static struct i2c_adapter *piix4_aux_adapter;
>  
>  static int piix4_add_adapter(struct pci_dev *dev, unsigned short smba,
> -			     bool sb800_main, u8 port,
> +			     bool sb800_main, u8 port, bool notify_imc,
>  			     const char *name, struct i2c_adapter **padap)
>  {
>  	struct i2c_adapter *adap;
> @@ -707,6 +767,7 @@ static int piix4_add_adapter(struct pci_dev *dev, unsigned short smba,
>  	adapdata->smba = smba;
>  	adapdata->sb800_main = sb800_main;
>  	adapdata->port = port << 1;
> +	adapdata->notify_imc = notify_imc;
>  
>  	/* set up the sysfs linkage to our parent device */
>  	adap->dev.parent = &dev->dev;
> @@ -728,14 +789,15 @@ static int piix4_add_adapter(struct pci_dev *dev, unsigned short smba,
>  	return 0;
>  }
>  
> -static int piix4_add_adapters_sb800(struct pci_dev *dev, unsigned short smba)
> +static int piix4_add_adapters_sb800(struct pci_dev *dev, unsigned short smba,
> +				    bool notify_imc)
>  {
>  	struct i2c_piix4_adapdata *adapdata;
>  	int port;
>  	int retval;
>  
>  	for (port = 0; port < PIIX4_MAX_ADAPTERS; port++) {
> -		retval = piix4_add_adapter(dev, smba, true, port,
> +		retval = piix4_add_adapter(dev, smba, true, port, notify_imc,
>  					   piix4_main_port_names_sb800[port],
>  					   &piix4_main_adapters[port]);
>  		if (retval < 0)
> @@ -769,6 +831,7 @@ static int piix4_probe(struct pci_dev *dev, const struct pci_device_id *id)
>  	     dev->device == PCI_DEVICE_ID_ATI_SBX00_SMBUS &&
>  	     dev->revision >= 0x40) ||
>  	    dev->vendor == PCI_VENDOR_ID_AMD) {
> +		bool notify_imc = false;
>  		is_sb800 = true;
>  
>  		if (!request_region(SB800_PIIX4_SMB_IDX, 2, "smba_idx")) {
> @@ -778,6 +841,18 @@ static int piix4_probe(struct pci_dev *dev, const struct pci_device_id *id)
>  			return -EBUSY;
>  		}
>  
> +		if (dev->vendor == PCI_VENDOR_ID_AMD &&
> +		    dev->device == PCI_DEVICE_ID_AMD_KERNCZ_SMBUS) {
> +			if (!devm_request_region(&dev->dev, IMC_SMB_IDX, 2,
> +						 "kerncz_imc_idx")) {
> +				dev_warn(&dev->dev,
> +					"IMC base address index region 0x%x already in use!\n",
> +					SB800_PIIX4_SMB_IDX);

How is the IMC related with the SMBus? I'm surprised that you touch the
IMC right from the SMBus driver like that. I'd expect other device
drivers to potentially have similar needs, which would require sharing
the region and proper locking.

Not blocking, but mixing managed and non-managed resources in the same
driver is not so nice.

> +			} else {
> +				notify_imc = true;
> +			}
> +		}
> +
>  		/* base address location etc changed in SB800 */
>  		retval = piix4_setup_sb800(dev, id, 0);
>  		if (retval < 0) {
> @@ -789,7 +864,7 @@ static int piix4_probe(struct pci_dev *dev, const struct pci_device_id *id)
>  		 * Try to register multiplexed main SMBus adapter,
>  		 * give up if we can't
>  		 */
> -		retval = piix4_add_adapters_sb800(dev, retval);
> +		retval = piix4_add_adapters_sb800(dev, retval, notify_imc);
>  		if (retval < 0) {
>  			release_region(SB800_PIIX4_SMB_IDX, 2);
>  			return retval;
> @@ -800,7 +875,7 @@ static int piix4_probe(struct pci_dev *dev, const struct pci_device_id *id)
>  			return retval;
>  
>  		/* Try to register main SMBus adapter, give up if we can't */
> -		retval = piix4_add_adapter(dev, retval, false, 0, "",
> +		retval = piix4_add_adapter(dev, retval, false, 0, false, "",
>  					   &piix4_main_adapters[0]);
>  		if (retval < 0)
>  			return retval;
> @@ -827,7 +902,7 @@ static int piix4_probe(struct pci_dev *dev, const struct pci_device_id *id)
>  	if (retval > 0) {
>  		/* Try to add the aux adapter if it exists,
>  		 * piix4_add_adapter will clean up if this fails */
> -		piix4_add_adapter(dev, retval, false, 0,
> +		piix4_add_adapter(dev, retval, false, 0, false,
>  				  is_sb800 ? piix4_aux_port_name_sb800 : "",
>  				  &piix4_aux_adapter);
>  	}


-- 
Jean Delvare
SUSE L3 Support

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