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@xxxxxxxxxx> > > > --- > > > 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
