Re: [PATCH 2/2] i2c: qcom-geni: Provide an option to disable DMA processing

[Lee Jones <lee.jones@linaro.org>]

On Thu, 05 Sep 2019, Marc Gonzalez wrote:

> [ Trimming recipients list for idle chat ]
> 
> On 05/09/2019 09:52, Lee Jones wrote:
> 
> > We have a production-level laptop (Lenovo Yoga C630) which is exhibiting
> > a rather horrific bug.  When I2C HID devices are being scanned for at
> > boot-time the QCom Geni based I2C (Serial Engine) attempts to use DMA.
> > When it does, the laptop reboots and the user never sees the OS.
> > 
> > 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* will not work - but they do not work now anyway.
> > 
> > Fixes: 8bc529b25354 ("soc: qcom: geni: Add support for ACPI")
> > Signed-off-by: Lee Jones <lee.jones@linaro.org>
> > Reviewed-by: Vinod Koul <vkoul@kernel.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..8822dea82980 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-no-dma"))
> > +		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-no-dma"))
> > +		dma_buf = i2c_get_dma_safe_msg_buf(msg, 32);
> > +
> >  	if (dma_buf)
> >  		geni_se_select_mode(se, GENI_SE_DMA);
> >  	else
> > 
> 
> Would it make sense to factorize the DT lookup within a helper?
> (For example; not compile-tested; not sure it's worth it)

Possibly, but the semantics end up the same.

If you think it's cleaner, perhaps submit your version a fix-up to the
original (this one).  Seeing as we're already carrying Reviewed-bys
and time is very limited to have this fixed.

I would also like to see the helper in your version prefixed, so it
would be:

  geni_i2c_get_dma_buf()

> diff --git a/drivers/i2c/busses/i2c-qcom-geni.c b/drivers/i2c/busses/i2c-qcom-geni.c
> index a89bfce5388e..1489181f60fe 100644
> --- a/drivers/i2c/busses/i2c-qcom-geni.c
> +++ b/drivers/i2c/busses/i2c-qcom-geni.c
> @@ -350,6 +350,14 @@ static void geni_i2c_tx_fsm_rst(struct geni_i2c_dev *gi2c)
>  		dev_err(gi2c->se.dev, "Timeout resetting TX_FSM\n");
>  }
>  
> +static void *get_dma_buf(struct geni_se *se, struct i2c_msg *msg)
> +{
> +	if (of_property_read_bool(se->dev->of_node, "qcom,geni-se-no-dma"))
> +		return NULL;
> +
> +	return i2c_get_dma_safe_msg_buf(msg, 32);
> +}
> +
>  static int geni_i2c_rx_one_msg(struct geni_i2c_dev *gi2c, struct i2c_msg *msg,
>  				u32 m_param)
>  {
> @@ -359,7 +367,7 @@ static int geni_i2c_rx_one_msg(struct geni_i2c_dev *gi2c, struct i2c_msg *msg,
>  	struct geni_se *se = &gi2c->se;
>  	size_t len = msg->len;
>  
> -	dma_buf = i2c_get_dma_safe_msg_buf(msg, 32);
> +	dma_buf = get_dma_buf(se, msg);
>  	if (dma_buf)
>  		geni_se_select_mode(se, GENI_SE_DMA);
>  	else
> @@ -398,7 +406,7 @@ static int geni_i2c_tx_one_msg(struct geni_i2c_dev *gi2c, struct i2c_msg *msg,
>  	struct geni_se *se = &gi2c->se;
>  	size_t len = msg->len;
>  
> -	dma_buf = i2c_get_dma_safe_msg_buf(msg, 32);
> +	dma_buf = get_dma_buf(se, msg);
>  	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
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