From: Lee Jones <lee.jones@linaro.org>
To: Wolfram Sang <wsa@the-dreams.de>
Cc: mark.rutland@arm.com, devicetree@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
agross@kernel.org, robh+dt@kernel.org,
Bjorn Andersson <bjorn.andersson@linaro.org>,
alokc@codeaurora.org, linux-i2c@vger.kernel.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 1/2] i2c: qcom-geni: Provide an option to select FIFO processing
Date: Thu, 5 Sep 2019 08:11:03 +0100 [thread overview]
Message-ID: <20190905071103.GX26880@dell> (raw)
In-Reply-To: <20190904212337.GF23608@ninjato>
On Wed, 04 Sep 2019, Wolfram Sang wrote:
> On Wed, Sep 04, 2019 at 01:35:48PM -0700, Bjorn Andersson wrote:
> > On Wed 04 Sep 04:36 PDT 2019, Lee Jones wrote:
> >
> > The subject implies that we select FIFO mode instead of DMA, but that's
> > not really true, because with DMA enabled we still fall back to FIFO for
> > messages below 32 bytes.
Do you mean, we fall back to DMA?
> > So what this does it to disable DMA, which neither the subject or the DT
> > property describes.
> >
> > Also missing is a description of why this is needed.
>
> Yes.
>
> I am willing to help to get this resolved soonish. However, I have
> issues with the approach.
>
> It looks like a workaround to me. It would be interesting to hear which
> I2C client breaks with DMA and if it's driver can't be fixed somehow
> instead. But even if we agree on a workaround short term, adding a
> binding for this workaround seems like a no-go to me. We have to live
> with this binding forever. Sidenote: I could think of a generic
> 'disable-dma' which could be reused everywhere but we probably won't get
> that upstream that late in the cycle.
>
> Is there no other way to disable DMA which is local to this driver so we
> can easily revert the workaround later?
This is the most local low-impact solution (nomenclature aside).
The beautiful thing about this approach is that, *if* the Geni SE DMA
ever starts working, we can remove the C code and any old properties
left in older DTs just become NOOP. Older kernels with newer DTs
(less of a priority) *still* won't work, but they don't work now
anyway.
NB: QCom have also made it pretty clear that DTBs *must* match their
kernel version. I know this is controversial amongst DT purists, but
it's still how QCom operate.
The offending line can be found at [0]. There is no obvious bug to
fix and this code obviously works well on some of the hardware
platforms using it. But on our platform (Lenovo Yoga C630 - QCom
SMD850) that final command, which initiates the DMA transaction, ends
up rebooting the machine.
With regards to the nomenclature, my original suggestion was
'qcom,geni-se-no-dma'. Would that better suit your request?
[0] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/soc/qcom/qcom-geni-se.c#n644
> > > Signed-off-by: Lee Jones <lee.jones@linaro.org>
> > > ---
> > > drivers/i2c/busses/i2c-qcom-geni.c | 14 ++++++++++----
> > > 1 file changed, 10 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/i2c/busses/i2c-qcom-geni.c b/drivers/i2c/busses/i2c-qcom-geni.c
> > > index a89bfce5388e..dfdbce067827 100644
> > > --- a/drivers/i2c/busses/i2c-qcom-geni.c
> > > +++ b/drivers/i2c/busses/i2c-qcom-geni.c
> > > @@ -353,13 +353,16 @@ static void geni_i2c_tx_fsm_rst(struct geni_i2c_dev *gi2c)
> > > static int geni_i2c_rx_one_msg(struct geni_i2c_dev *gi2c, struct i2c_msg *msg,
> > > u32 m_param)
> > > {
> > > + struct device_node *np = gi2c->se.dev->of_node;
> > > dma_addr_t rx_dma;
> > > unsigned long time_left;
> > > - void *dma_buf;
> > > + void *dma_buf = NULL;
> > > struct geni_se *se = &gi2c->se;
> > > size_t len = msg->len;
> > >
> > > - dma_buf = i2c_get_dma_safe_msg_buf(msg, 32);
> > > + if (!of_property_read_bool(np, "qcom,geni-se-fifo"))
> > > + dma_buf = i2c_get_dma_safe_msg_buf(msg, 32);
> > > +
> > > if (dma_buf)
> > > geni_se_select_mode(se, GENI_SE_DMA);
> > > else
> > > @@ -392,13 +395,16 @@ static int geni_i2c_rx_one_msg(struct geni_i2c_dev *gi2c, struct i2c_msg *msg,
> > > static int geni_i2c_tx_one_msg(struct geni_i2c_dev *gi2c, struct i2c_msg *msg,
> > > u32 m_param)
> > > {
> > > + struct device_node *np = gi2c->se.dev->of_node;
> > > dma_addr_t tx_dma;
> > > unsigned long time_left;
> > > - void *dma_buf;
> > > + void *dma_buf = NULL;
> > > struct geni_se *se = &gi2c->se;
> > > size_t len = msg->len;
> > >
> > > - dma_buf = i2c_get_dma_safe_msg_buf(msg, 32);
> > > + if (!of_property_read_bool(np, "qcom,geni-se-fifo"))
> > > + dma_buf = i2c_get_dma_safe_msg_buf(msg, 32);
> > > +
> > > if (dma_buf)
> > > geni_se_select_mode(se, GENI_SE_DMA);
> > > else
--
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog
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next prev parent reply other threads:[~2019-09-05 7:11 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-04 11:36 [PATCH 1/2] i2c: qcom-geni: Provide an option to select FIFO processing Lee Jones
2019-09-04 11:36 ` [PATCH 2/2] dt-bindings: soc: qcom: Provide option to select FIFO mode Lee Jones
2019-09-04 11:58 ` Vinod Koul
2019-09-04 11:56 ` [PATCH 1/2] i2c: qcom-geni: Provide an option to select FIFO processing Vinod Koul
2019-09-04 12:18 ` Lee Jones
2019-09-04 11:58 ` Vinod Koul
2019-09-04 20:35 ` Bjorn Andersson
2019-09-04 21:23 ` Wolfram Sang
2019-09-05 7:11 ` Lee Jones [this message]
2019-09-05 9:16 ` Wolfram Sang
2019-09-05 9:34 ` Lee Jones
2019-09-05 13:37 ` Wolfram Sang
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