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Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hb1Zh-0003q4-AH; Wed, 12 Jun 2019 11:37:53 +0000 Received: from bhuna.collabora.co.uk ([2a00:1098:0:82:1000:25:2eeb:e3e3]) by bombadil.infradead.org with esmtps (Exim 4.92 #3 (Red Hat Linux)) id 1hb1ZM-0003VL-Tk for linux-i3c@lists.infradead.org; Wed, 12 Jun 2019 11:37:35 +0000 Received: from localhost (unknown [IPv6:2a01:e0a:2c:6930:5cf4:84a1:2763:fe0d]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) (Authenticated sender: bbrezillon) by bhuna.collabora.co.uk (Postfix) with ESMTPSA id 92630260269; Wed, 12 Jun 2019 12:37:30 +0100 (BST) Date: Wed, 12 Jun 2019 13:37:27 +0200 From: Boris Brezillon To: Vitor Soares Subject: Re: [PATCH v3 1/3] i3c: fix i2c and i3c scl rate by bus mode Message-ID: <20190612133727.48f85060@collabora.com> In-Reply-To: <13D59CF9CEBAF94592A12E8AE55501350AABEC91@DE02WEMBXB.internal.synopsys.com> References: <20190612081533.2cf9e12a@collabora.com> <13D59CF9CEBAF94592A12E8AE55501350AABEC91@DE02WEMBXB.internal.synopsys.com> Organization: Collabora X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-redhat-linux-gnu) MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190612_043733_244359_8D37BAAB X-CRM114-Status: GOOD ( 30.69 ) X-BeenThere: linux-i3c@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux I3C List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "linux-i3c@lists.infradead.org" , "Joao.Pinto@synopsys.com" , "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" , Boris Brezillon Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-i3c" Errors-To: linux-i3c-bounces+linux-i3c=archiver.kernel.org@lists.infradead.org On Wed, 12 Jun 2019 11:16:34 +0000 Vitor Soares wrote: > From: Boris Brezillon > Date: Wed, Jun 12, 2019 at 07:15:33 > > > On Tue, 11 Jun 2019 16:06:43 +0200 > > Vitor Soares wrote: > > > > > Currently the I3C framework limits SCL frequency to FM speed when > > > dealing with a mixed slow bus, even if all I2C devices are FM+ capable. > > > > > > The core was also not accounting for I3C speed limitations when > > > operating in mixed slow mode and was erroneously using FM+ speed as the > > > max I2C speed when operating in mixed fast mode. > > > > > > Fixes: 3a379bbcea0a ("i3c: Add core I3C infrastructure") > > > Signed-off-by: Vitor Soares > > > Cc: Boris Brezillon > > > Cc: > > > Cc: > > > --- > > > Changes in v3: > > > Change dev_warn() to dev_dbg() > > > > > > Changes in v2: > > > Enhance commit message > > > Add dev_warn() in case user-defined i2c rate doesn't match LVR constraint > > > Add dev_warn() in case user-defined i3c rate lower than i2c rate > > > > > > drivers/i3c/master.c | 61 +++++++++++++++++++++++++++++++++++++++++----------- > > > 1 file changed, 48 insertions(+), 13 deletions(-) > > > > > > diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c > > > index 5f4bd52..f8e580e 100644 > > > --- a/drivers/i3c/master.c > > > +++ b/drivers/i3c/master.c > > > @@ -91,6 +91,12 @@ void i3c_bus_normaluse_unlock(struct i3c_bus *bus) > > > up_read(&bus->lock); > > > } > > > > > > +static struct i3c_master_controller * > > > +i3c_bus_to_i3c_master(struct i3c_bus *i3cbus) > > > +{ > > > + return container_of(i3cbus, struct i3c_master_controller, bus); > > > +} > > > + > > > static struct i3c_master_controller *dev_to_i3cmaster(struct device *dev) > > > { > > > return container_of(dev, struct i3c_master_controller, dev); > > > @@ -565,20 +571,48 @@ static const struct device_type i3c_masterdev_type = { > > > .groups = i3c_masterdev_groups, > > > }; > > > > > > -int i3c_bus_set_mode(struct i3c_bus *i3cbus, enum i3c_bus_mode mode) > > > +int i3c_bus_set_mode(struct i3c_bus *i3cbus, enum i3c_bus_mode mode, > > > + unsigned long max_i2c_scl_rate) > > > { > > > - i3cbus->mode = mode; > > > > > > - if (!i3cbus->scl_rate.i3c) > > > - i3cbus->scl_rate.i3c = I3C_BUS_TYP_I3C_SCL_RATE; > > > + struct i3c_master_controller *master = i3c_bus_to_i3c_master(i3cbus); > > > > > > - if (!i3cbus->scl_rate.i2c) { > > > - if (i3cbus->mode == I3C_BUS_MODE_MIXED_SLOW) > > > - i3cbus->scl_rate.i2c = I3C_BUS_I2C_FM_SCL_RATE; > > > - else > > > - i3cbus->scl_rate.i2c = I3C_BUS_I2C_FM_PLUS_SCL_RATE; > > > + i3cbus->mode = mode; > > > + > > > + switch (i3cbus->mode) { > > > + case I3C_BUS_MODE_PURE: > > > + if (!i3cbus->scl_rate.i3c) > > > + i3cbus->scl_rate.i3c = I3C_BUS_TYP_I3C_SCL_RATE; > > > + break; > > > + case I3C_BUS_MODE_MIXED_FAST: > > > + if (!i3cbus->scl_rate.i3c) > > > + i3cbus->scl_rate.i3c = I3C_BUS_TYP_I3C_SCL_RATE; > > > + if (!i3cbus->scl_rate.i2c) > > > + i3cbus->scl_rate.i2c = max_i2c_scl_rate; > > > + break; > > > + case I3C_BUS_MODE_MIXED_SLOW: > > > + if (!i3cbus->scl_rate.i2c) > > > + i3cbus->scl_rate.i2c = max_i2c_scl_rate; > > > + if (!i3cbus->scl_rate.i3c || > > > + i3cbus->scl_rate.i3c > i3cbus->scl_rate.i2c) > > > + i3cbus->scl_rate.i3c = i3cbus->scl_rate.i2c; > > > + break; > > > + default: > > > + return -EINVAL; > > > } > > > > > > + if (i3cbus->scl_rate.i3c < i3cbus->scl_rate.i2c) > > > + dev_dbg(&master->dev, > > > + "i3c-scl-hz=%ld lower than i2c-scl-hz=%ld\n", > > > + i3cbus->scl_rate.i3c, i3cbus->scl_rate.i2c); > > > + > > > + if (i3cbus->scl_rate.i2c != I3C_BUS_I2C_FM_SCL_RATE && > > > + i3cbus->scl_rate.i2c != I3C_BUS_I2C_FM_PLUS_SCL_RATE && > > > + i3cbus->mode != I3C_BUS_MODE_PURE) > > > + dev_dbg(&master->dev, > > > + "i2c-scl-hz=%ld not defined according MIPI I3C spec\n", > > > + i3cbus->scl_rate.i2c); > > > + > > > > Again, that's not what I suggested, so I'll write it down: > > > > dev_dbg(&master->dev, "i2c-scl = %ld Hz i3c-scl = %ld Hz\n", > > i3cbus->scl_rate.i2c, i3cbus->scl_rate.i3c); > > > > I'm not ok with that change. The reasons are: > i3cbus->scl_rate.i3c < i3cbus->scl_rate.i2c is an abnormal use case. As > discuss early it can be cause by a wrong DT definition or just for > testing purposes. Is it buggy, and if it is, what are the symptoms? And I'm not talking about slow transfers here. Also, note that forcing the I2C/I3C rate through the DT already means you want to tweak the bus speed (either for debugging purposes or because slowing things down is needed to fix a HW bug). > > i3cbus->scl_rate.i2c != I3C_BUS_I2C_FM_SCL_RATE && i3cbus->scl_rate.i2c > != I3C_BUS_I2C_FM_PLUS_SCL_RATE, the MIPI I3C Spec v1.0 clearly says that > all I2C devices on the bus shall have a LVR register and thus support FM > or FM+ modes. Yet, you might want to apply a lower I2C freq, and this sounds like a valid case that doesn't deserve a dev_warn(). > By definition a FM bus works at 400kHz and a FM+ bus 1MHz. > And for slaves, a FM device works up to 400kHz and a FM+ device works up > to 1MHz respectively. *up to*, that's the important thing to keep in mind. There's no problem driving the SCL signal at a lower freq. > > Apart of that, if the I2C device support you can use a custom higher or > lower rate, yet not defined according MIPI I3C spec. I'm not going to have this discussion again, sorry. I think I gave enough arguments to explain why having an I2C SLC rate that's slower than what I2C devices support is fine. > > > dev_dbg() is not printed by default, so it's just fine to have a trace > > that prints the I3C and I2C rate unconditionally. > > I'm ok to change the way that user is notified and I think that is here > the problem. > Maybe the best is to change the first dev_dbg() to dev_warn() and the > second dev_info(). Same here. I'm fine having a dev_warn() when the rate is higher than what's supported by devices present on the bus (because that case is buggy), but not when it's lower and still in the valid range. _______________________________________________ linux-i3c mailing list linux-i3c@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-i3c