RE: [PATCH v6 4/5] i2c: aspeed: added driver for Aspeed I2C

[Ryan Chen <ryan_chen-SAlXDmAnmOAqDJ6do+/SaQ@public.gmane.org>]

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Thanks Ryan. Can you shed some light on the meaning of the high-speed bit as well please ?

About ASPEED_I2CD_M_HIGH_SPEED_EN, it is support for I2C specification "High speed transfer". And also device need support it. 
If you just speed up the I2C bus clock, you don’t have to enable ASPEED_I2CD_M_HIGH_SPEED_EN, just change the clock is ok.


-----Original Message-----
From: Benjamin Herrenschmidt [mailto:benh@kernel.crashing.org] 
Sent: Tuesday, April 25, 2017 5:35 PM
To: Ryan Chen <ryan_chen@aspeedtech.com>; Brendan Higgins <brendanhiggins@google.com>
Cc: Wolfram Sang <wsa@the-dreams.de>; Rob Herring <robh+dt@kernel.org>; Mark Rutland <mark.rutland@arm.com>; Thomas Gleixner <tglx@linutronix.de>; Jason Cooper <jason@lakedaemon.net>; Marc Zyngier <marc.zyngier@arm.com>; Joel Stanley <joel@jms.id.au>; Vladimir Zapolskiy <vz@mleia.com>; Kachalov Anton <mouse@mayc.ru>; Cédric Le Goater <clg@kaod.org>; linux-i2c@vger.kernel.org; devicetree@vger.kernel.org; Linux Kernel Mailing List <linux-kernel@vger.kernel.org>; OpenBMC Maillist <openbmc@lists.ozlabs.org>
Subject: Re: [PATCH v6 4/5] i2c: aspeed: added driver for Aspeed I2C

On Tue, 2017-04-25 at 08:50 +0000, Ryan Chen wrote:
> Hello All,
> 		ASPEED_I2CD_M_SDA_DRIVE_1T_EN,
> ASPEED_I2CD_SDA_DRIVE_1T_EN is specific for some case usage. 
> 		For example, if i2c bus is use on "high speed" and "single slave and 
> master" and i2c bus is too long. It need drive SDA or SCL less lunacy. 
> It would enable it.
> 		Otherwise, don’t enable it. especially in multi-master. 
> It can’t be enable.

That smells like a specific enough use case that we should probably cover with a device-tree property, something like an empty "sda-extra-drive" property (empty properties are typically used for booleans, their presence means "true").

Thanks Ryan. Can you shed some light on the meaning of the high-speed bit as well please ? Does it force to a specific speed (ignoring the
divisor) or we can still play with the clock high/low counts ?

Cheers,
Ben.

> 		  
> 	
> 
> Best Regards,
> Ryan
> 
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> -----Original Message-----
> From: Brendan Higgins [mailto:brendanhiggins@google.com]
> Sent: Tuesday, April 25, 2017 4:32 PM
> To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Wolfram Sang <wsa@the-dreams.de>; Rob Herring <robh+dt@kernel.org
> >; Mark Rutland <mark.rutland@arm.com>; Thomas Gleixner <tglx@linutro
> nix.de>; Jason Cooper <jason@lakedaemon.net>; Marc Zyngier <marc.zyng 
> ier@arm.com>; Joel Stanley <joel@jms.id.au>; Vladimir Zapolskiy <vz@m 
> leia.com>; Kachalov Anton <mouse@mayc.ru>; Cédric Le Goater <clg@kaod 
> .org>; linux-i2c@vger.kernel.org; devicetree@vger.kernel.org; Linux 
> Kernel Mailing List <linux-kernel@vger.kernel.org>; OpenBMC Maillist 
> <openbmc@lists.ozlabs.org>; Ryan Chen <ryan_chen@aspeedtech.com>
> Subject: Re: [PATCH v6 4/5] i2c: aspeed: added driver for Aspeed I2C
> 
> Adding Ryan.
> 
> On Mon, Apr 24, 2017 at 7:19 PM, Benjamin Herrenschmidt <benh@kernel.
> crashing.org> wrote:
> > On Mon, 2017-04-24 at 11:56 -0700, Brendan Higgins wrote:
> > > > > +struct aspeed_i2c_bus {
> > > > > +     struct i2c_adapter              adap;
> > > > > +     struct device                   *dev;
> > > > > +     void __iomem                    *base;
> > > > > +     /* Synchronizes I/O mem access to base. */
> > > > > +     spinlock_t                      lock;
> > > > 
> > > > I am not entirely convinced we need that lock. The i2c core will 
> > > > take a mutex protecting all operations on the bus. So we only 
> > > > need to synchronize between our "xfer" code and our interrupt 
> > > > handler.
> > > 
> > > You are right if both having slave and master active at the same 
> > > time was not possible; however, it is.
> > 
> > Right, I somewhat forgot about the slave case.
> > 
> >   ...
> > 
> > > > Some of those error states probably also warrant a reset of the 
> > > > controller, I think aspeed does that in the SDK.
> > > 
> > > For timeout and cmd_err, I do not see any argument against it; it 
> > > sounds like we are in a very messed up, very unknown state, so 
> > > full reset is probably the best last resort.
> > 
> > Yup.
> > 
> > > For SDA staying pulled down, I
> > > think we can say with reasonable confidence that some device on 
> > > our bus is behaving very badly and I am not convinced that 
> > > resetting the controller is likely to do anything to help;
> > 
> > Right. Hammering with STOPs and pray ...
> 
> I think sending recovery mode sends stops as a part of the recovery 
> algorithm it executes.
> 
> > 
> > >  that being said, I really
> > > do not have any good ideas to address that. So maybe praying and 
> > > resetting the controller is *the most reasonable thing to do.* I 
> > > would like to know what you think we should do in that case.
> > 
> > Well, there's a (small ?) chance that it's a controller bug 
> > asserting the line so ... but there's little we can do if not.
> 
> True.
> 
> > 
> > > While I was thinking about this I also realized that the SDA line 
> > > check after recovery happens in the else branch, but SCL line 
> > > check does not happen after we attempt to STOP if SCL is hung. If 
> > > we decide to make special note SDA being hung by a device that 
> > > won't let go, we might want to make a special note that SCL is 
> > > hung by a device that won't let go. Just a thought.
> > 
> > Maybe. Or just "unrecoverable error"... hopefully these don't happen 
> > too often ... We had cases of a TPM misbehaving like that.
> 
> Yeah, definitely should print something out.
> 
> > 
> > > > > +out:
> > > 
> > > ...
> > > > What about I2C_M_NOSTART ?
> > > > 
> > > > Not that I've ever seen it used... ;-)
> > > 
> > > Right now I am not doing any of the protocol mangling options, but 
> > > I can add them in if you think it is important for initial 
> > > support.
> > 
> > No, not important, we can add that later if it ever becomes useful.
> > 
> >  ...
> > 
> > > > In general, you always ACK all interrupts first. Then you handle 
> > > > the bits you have harvested.
> > > > 
> > > 
> > > The documentation says to ACK the interrupt after handling in the 
> > > RX
> > > case:
> > > 
> > > <<<
> > > S/W needs to clear this status bit to allow next data receiving.
> > > > > > 
> > > 
> > > I will double check with Ryan to make sure TX works the same way.
> > > 
> > > > > +     if (irq_status & ASPEED_I2CD_INTR_ERROR ||
> > > > > +         (!bus->msgs && bus->master_state !=
> > > > > ASPEED_I2C_MASTER_STOP)) {
> > > 
> > > ...
> > > > 
> > > > I would set master_state to "RECOVERY" (new state ?) and ensure 
> > > > those things are caught if they happen outside of a recovery.
> > 
> > I replied privately ... as long as we ack before we start a new 
> > command we should be ok but we shouldn't ack after.
> > 
> > Your latest patch still does that. It will do things like start a 
> > STOP command *then* ack the status bits. I'm pretty sure that's 
> > bogus.
> > 
> > That way it's a lot simpler to simply move the
> > 
> >         writel(irq_status, bus->base + ASPEED_I2C_INTR_STS_REG);
> > 
> > To either right after the readl of the status reg at the beginning 
> > of aspeed_i2c_master_irq().
> > 
> > I would be very surprised if that didn't work properly and wasn't 
> > much safer than what you are currently doing.
> 
> I think I tried your way and it worked. In anycase, Ryan will be able 
> to clarify for us.
> 
> > 
> > > Let me know if you still think we need a "RECOVERY" state.
> > 
> > The way you just switch to stop state and store the error for later 
> > should work I think.
> > 
> > > > 
> > > > > +     if (bus->master_state == ASPEED_I2C_MASTER_START) {
> > > 
> > > ...
> > > > 
> > > > > +                     dev_dbg(bus->dev,
> > > > > +                             "no slave present at %02x",
> > > > > msg-
> > > > > > addr);
> > > > > 
> > > > > +                     status_ack |= ASPEED_I2CD_INTR_TX_NAK;
> > > > > +                     bus->cmd_err = -EIO;
> > > > > +                     do_stop(bus);
> > > > > +                     goto out_no_complete;
> > > > > +             } else {
> > > > > +                     status_ack |= ASPEED_I2CD_INTR_TX_ACK;
> > > > > +                     if (msg->flags & I2C_M_RD)
> > > > > +                             bus->master_state =
> > > > > ASPEED_I2C_MASTER_RX;
> > > > > +                     else
> > > > > +                             bus->master_state =
> > > > > ASPEED_I2C_MASTER_TX_FIRST;
> > > > 
> > > > What about the SMBUS_QUICK case ? (0-len transfer). Do we need 
> > > > to handle this here ? A quick look at the TX_FIRST case makes me 
> > > > think we are ok there but I'm not sure about the RX case.
> > > 
> > > I did not think that there is an SMBUS_QUICK RX. Could you point 
> > > me to an example?
> > 
> > Not so much an RX, it's more like you are sending a 1-bit data in 
> > the place of the Rd/Wr bit. So you have a read with a lenght of 0, I 
> > don't think in that case you should set ASPEED_I2CD_M_RX_CMD in 
> > __aspeed_i2c_do_start
> 
> Forget what I said, I was just not thinking about the fact that SMBus 
> emulation causes the data bit to be encoded as the R/W flag. I see 
> what you are saying; you are correct.
> 
> > 
> > > > I'm not sure the RX case is tight also. What completion does the 
> > > > HW give you for the address cycle ? Won't you get that before it 
> > > > has received the first character ? IE. You fall through to the 
> > > > read case of the state machine with the read potentially not 
> > > > complete yet no ?
> > > 
> > > ...
> > > > > +     case ASPEED_I2C_MASTER_RX:
> > > > > +             if (!(irq_status & ASPEED_I2CD_INTR_RX_DONE)) {
> > > > > +                     dev_err(bus->dev, "master failed to
> > > > > RX");
> > > > > +                     goto out_complete;
> > > > > +             }
> > > > 
> > > > See my comment above for a bog standard i2c_read. Aren't you 
> > > > getting the completion for the address before the read is even 
> > > > started ?
> > > 
> > > In practice no, but it is probably best to be safe :-)
> > 
> > Yup :)
> > > > 
> > > > > +             status_ack |= ASPEED_I2CD_INTR_RX_DONE;
> > > > > +
> > > > > +             recv_byte = aspeed_i2c_read(bus,
> > > > > ASPEED_I2C_BYTE_BUF_REG) >> 8;
> > > > > +             msg->buf[bus->buf_index++] = recv_byte;
> > > > > +
> > > > > +             if (msg->flags & I2C_M_RECV_LEN &&
> > > > > +                 recv_byte <= I2C_SMBUS_BLOCK_MAX) {
> > > > > +                     msg->len = recv_byte +
> > > > > +                                     ((msg->flags &
> > > > > I2C_CLIENT_PEC) ? 2 : 1);
> > > 
> > > ...
> > > > > +     return ((clk_high << ASPEED_I2CD_TIME_SCL_HIGH_SHIFT)
> > > > > +             & ASPEED_I2CD_TIME_SCL_HIGH_MASK)
> > > > > +                     | ((clk_low <<
> > > > > ASPEED_I2CD_TIME_SCL_LOW_SHIFT)
> > > > > +                        & ASPEED_I2CD_TIME_SCL_LOW_MASK)
> > > > > +                     | (base_clk &
> > > > > ASPEED_I2CD_TIME_BASE_DIVISOR_MASK);
> > > > > +}
> > > > 
> > > > As I think I mentioned earlier, the AST2500 has a slightly 
> > > > different register layout which support larger values for high 
> > > > and low, thus allowing a finer granularity.
> > > 
> > > I am developing against the 2500.
> > 
> > Yes but we'd like the driver to work with both :-)
> 
> Right, I thought you were making an assertion about the 2500, if you 
> are making an assertion about the 2400, I do not know and do not have 
> one handy.
> 
> > 
> > > > BTW. In case you haven't, I would suggest you copy/paste the 
> > > > above in a userspace app and run it for all frequency divisors 
> > > > and see if your results match the aspeed table :)
> > > 
> > > Good call.
> > 
> > If you end up doing that, can you shoot it my way ? I can take care 
> > of making sure it's all good for the 2400.
> 
> Will do.
> 
> > 
> > > > > +static int aspeed_i2c_init_clk(struct aspeed_i2c_bus *bus,
> > > > > +                            struct platform_device *pdev) {
> > > > > +     u32 clk_freq, divisor;
> > > > > +     struct clk *pclk;
> > > > > +     int ret;
> > > > > +
> > > > > +     pclk = devm_clk_get(&pdev->dev, NULL);
> > > > > +     if (IS_ERR(pclk)) {
> > > > > +             dev_err(&pdev->dev, "clk_get failed\n");
> > > > > +             return PTR_ERR(pclk);
> > > > > +     }
> > > > > +     ret = of_property_read_u32(pdev->dev.of_node,
> > > > > +                                "clock-frequency",
> > > > > &clk_freq);
> > > > 
> > > > See my previous comment about calling that 'bus-frequency'
> > > > rather
> > > > than 'clock-frequency'.
> > > > 
> > > > > +     if (ret < 0) {
> > > > > +             dev_err(&pdev->dev,
> > > > > +                     "Could not read clock-frequency
> > > > > property\n");
> > > > > +             clk_freq = 100000;
> > > > > +     }
> > > > > +     divisor = clk_get_rate(pclk) / clk_freq;
> > > > > +     /* We just need the clock rate, we don't actually use
> > > > > the
> > > > > clk object. */
> > > > > +     devm_clk_put(&pdev->dev, pclk);
> > > > > +
> > > > > +     /* Set AC Timing */
> > > > > +     if (clk_freq / 1000 > 1000) {
> > > > > +             aspeed_i2c_write(bus, aspeed_i2c_read(bus,
> > > > > +                                                   ASPEED_I2
> > > > > C_FU
> > > > > N_CTRL_REG) |
> > > > > +                             ASPEED_I2CD_M_HIGH_SPEED_EN |
> > > > > +                             ASPEED_I2CD_M_SDA_DRIVE_1T_EN |
> > > > > +                             ASPEED_I2CD_SDA_DRIVE_1T_EN,
> > > > > +                             ASPEED_I2C_FUN_CTRL_REG);
> > > > > +
> > > > > +             aspeed_i2c_write(bus, 0x3,
> > > > > ASPEED_I2C_AC_TIMING_REG2);
> > > > > +             aspeed_i2c_write(bus,
> > > > > aspeed_i2c_get_clk_reg_val(divisor),
> > > > > +                              ASPEED_I2C_AC_TIMING_REG1);
> > > > 
> > > > I already discussed by doubts about the above. I can try to 
> > > > scope it with the EVB if you don't get to it. For now I'd rather 
> > > > take the code out.
> > > > 
> > > > We should ask aspeed from what frequency the "1T" stuff is 
> > > > useful.
> > > 
> > > Will do, I will try to rope Ryan in on the next review; it will be 
> > > good for him to get used to working with upstream anyway.
> > 
> > Yup. However, for the sake of getting something upstream (and in 
> > OpenBMC 4.10 kernel) asap, I would suggest just dropping support for 
> > those fast speeds for now, we can add them back later.
> 
> Alright, that's fine. Still, Ryan, could you provide some context on 
> this?
> 
> > 
> > > > 
> > > > > +     } else {
> > > > > +             aspeed_i2c_write(bus,
> > > > > aspeed_i2c_get_clk_reg_val(divisor),
> > > > > +                              ASPEED_I2C_AC_TIMING_REG1);
> > > > > +             aspeed_i2c_write(bus, ASPEED_NO_TIMEOUT_CTRL,
> > > > > +                              ASPEED_I2C_AC_TIMING_REG2);
> > > > > +     }
> > > 
> > > ...
> > > > > +     spin_lock_init(&bus->lock);
> > > > > +     init_completion(&bus->cmd_complete);
> > > > > +     bus->adap.owner = THIS_MODULE;
> > > > > +     bus->adap.retries = 0;
> > > > > +     bus->adap.timeout = 5 * HZ;
> > > > > +     bus->adap.algo = &aspeed_i2c_algo;
> > > > > +     bus->adap.algo_data = bus;
> > > > > +     bus->adap.dev.parent = &pdev->dev;
> > > > > +     bus->adap.dev.of_node = pdev->dev.of_node;
> > > > > +     snprintf(bus->adap.name, sizeof(bus->adap.name),
> > > > > "Aspeed
> > > > > i2c");
> > > > 
> > > > Another trivial one, should we put some kind of bus number in 
> > > > that string ?
> > > 
> > > Whoops, looks like I missed this one; I will get to it in the next 
> > > revision.
> > 
> > Ok. I noticed you missed that in v7, so I assume you mean v8 :-)
> 
> Yep, I will get it in v8.
> 
> > 
> > > > 
> > > > > +     bus->dev = &pdev->dev;
> > > > > +
> > > > > +     /* reset device: disable master & slave functions */
> > > > > +     aspeed_i2c_write(bus, 0, ASPEED_I2C_FUN_CTRL_REG);
> > > 
> > > ...
> > > --
> > > To unsubscribe from this list: send the line "unsubscribe 
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> > > in
> > > the body of a message to majordomo@vger.kernel.org More majordomo 
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