Re: [PATCH v3 3/4] i2c: sh_mobile: use helper to decide if DMA is useful

[Niklas Söderlund]

Hi Wolfram,

On 2017-07-18 12:23:38 +0200, Wolfram Sang wrote:
> This ensures that we fall back to PIO if the buffer is too small for DMA
> being useful. Otherwise, we use DMA. A bounce buffer might be applied if
> the original message buffer is not DMA safe
> 
> Signed-off-by: Wolfram Sang 
> ---
>  drivers/i2c/busses/i2c-sh_mobile.c | 8 ++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-sh_mobile.c 
> b/drivers/i2c/busses/i2c-sh_mobile.c
> index 2e097d97d258bc..19f45bcd9b35ca 100644
> --- a/drivers/i2c/busses/i2c-sh_mobile.c
> +++ b/drivers/i2c/busses/i2c-sh_mobile.c
> @@ -145,6 +145,7 @@ struct sh_mobile_i2c_data {
>   struct dma_chan *dma_rx;
>   struct scatterlist sg;
>   enum dma_data_direction dma_direction;
> + u8 *bounce_buf;
>  };
>  
>  struct sh_mobile_dt_config {
> @@ -548,6 +549,8 @@ static void sh_mobile_i2c_dma_callback(void *data)
>   pd->pos = pd->msg->len;
>   pd->stop_after_dma = true;
>  
> + i2c_release_dma_bounce_buf(pd->msg, pd->bounce_buf);
> +
>   iic_set_clr(pd, ICIC, 0, ICIC_TDMAE | ICIC_RDMAE);
>  }
>  
> @@ -595,6 +598,7 @@ static void sh_mobile_i2c_xfer_dma(struct 
> sh_mobile_i2c_data *pd)
>   struct dma_async_tx_descriptor *txdesc;
>   dma_addr_t dma_addr;
>   dma_cookie_t cookie;
> + u8 *dma_buf = pd->bounce_buf ?: pd->msg->buf;

This looked funny and I had to look it up, I learnt something new today 
:-)

>  
>   if (PTR_ERR(chan) == -EPROBE_DEFER) {
>   if (read)
> @@ -608,7 +612,7 @@ static void sh_mobile_i2c_xfer_dma(struct 
> sh_mobile_i2c_data *pd)
>   if (IS_ERR(chan))
>   return;
>  
> - dma_addr = dma_map_single(chan->device->dev, pd->msg->buf, 
> pd->msg->len, dir);
> + dma_addr = dma_map_single(chan->device->dev, dma_buf, pd->msg->len, 
> dir);
>   if (dma_mapping_error(chan->device->dev, dma_addr)) {
>   dev_dbg(pd->dev, "dma map failed, using PIO\n");
>   return;
> @@ -665,7 +669,7 @@ static int start_ch(struct sh_mobile_i2c_data *pd, struct 
> i2c_msg *usr_msg,
>   pd->pos = -1;
>   pd->sr = 0;
>  
> - if (pd->msg->len > 8)
> + if (i2c_check_msg_for_dma(pd->msg, 8, >bounce_buf) == 0)

Maybe the 8 should be declared in a define to explain the value, like 
you do in patch 4/4?

This nitpick aside:

Reviewed-by: Niklas Söderlund 

>   sh_mobile_i2c_xfer_dma(pd);
>  
>   /* Enable all interrupts to begin with */
> -- 
> 2.11.0
> 

-- 
Regards,
Niklas Söderlund

[PATCH v3 3/4] i2c: sh_mobile: use helper to decide if DMA is useful

[Wolfram Sang]

This ensures that we fall back to PIO if the buffer is too small for DMA
being useful. Otherwise, we use DMA. A bounce buffer might be applied if
the original message buffer is not DMA safe

Signed-off-by: Wolfram Sang 
---
 drivers/i2c/busses/i2c-sh_mobile.c | 8 ++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/busses/i2c-sh_mobile.c 
b/drivers/i2c/busses/i2c-sh_mobile.c
index 2e097d97d258bc..19f45bcd9b35ca 100644
--- a/drivers/i2c/busses/i2c-sh_mobile.c
+++ b/drivers/i2c/busses/i2c-sh_mobile.c
@@ -145,6 +145,7 @@ struct sh_mobile_i2c_data {
struct dma_chan *dma_rx;
struct scatterlist sg;
enum dma_data_direction dma_direction;
+   u8 *bounce_buf;
 };
 
 struct sh_mobile_dt_config {
@@ -548,6 +549,8 @@ static void sh_mobile_i2c_dma_callback(void *data)
pd->pos = pd->msg->len;
pd->stop_after_dma = true;
 
+   i2c_release_dma_bounce_buf(pd->msg, pd->bounce_buf);
+
iic_set_clr(pd, ICIC, 0, ICIC_TDMAE | ICIC_RDMAE);
 }
 
@@ -595,6 +598,7 @@ static void sh_mobile_i2c_xfer_dma(struct 
sh_mobile_i2c_data *pd)
struct dma_async_tx_descriptor *txdesc;
dma_addr_t dma_addr;
dma_cookie_t cookie;
+   u8 *dma_buf = pd->bounce_buf ?: pd->msg->buf;
 
if (PTR_ERR(chan) == -EPROBE_DEFER) {
if (read)
@@ -608,7 +612,7 @@ static void sh_mobile_i2c_xfer_dma(struct 
sh_mobile_i2c_data *pd)
if (IS_ERR(chan))
return;
 
-   dma_addr = dma_map_single(chan->device->dev, pd->msg->buf, 
pd->msg->len, dir);
+   dma_addr = dma_map_single(chan->device->dev, dma_buf, pd->msg->len, 
dir);
if (dma_mapping_error(chan->device->dev, dma_addr)) {
dev_dbg(pd->dev, "dma map failed, using PIO\n");
return;
@@ -665,7 +669,7 @@ static int start_ch(struct sh_mobile_i2c_data *pd, struct 
i2c_msg *usr_msg,
pd->pos = -1;
pd->sr = 0;
 
-   if (pd->msg->len > 8)
+   if (i2c_check_msg_for_dma(pd->msg, 8, >bounce_buf) == 0)
sh_mobile_i2c_xfer_dma(pd);
 
/* Enable all interrupts to begin with */
-- 
2.11.0