[v2,5/5] spi: s3c64xx: use unsigned type for fifo handling variables

Commit Message

Andi Shyti June 28, 2016, 2:41 a.m. UTC

The 'quirks' variable cannot ever be negative, therefore use u8
instead of int. The 8 bit size is given from the fact that
currently the quirks variable has very few statuses.

The rx_lvl_offset and tx_st_done store shift values, so that u8
is a proper size.

fifo_lvl_mask stores a series of masks, to be in we will keep the
32 bit size.

Signed-off-by: Andi Shyti <[e-mail]>
Signed-off-by: Jaehoon Chung <[e-mail]>
---
 drivers/spi/spi-s3c64xx.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

Comments

Mark Brown July 5, 2016, 2:55 p.m. UTC | #1

On Tue, Jun 28, 2016 at 11:41:15AM +0900, Andi Shyti wrote:
> The 'quirks' variable cannot ever be negative, therefore use u8
> instead of int. The 8 bit size is given from the fact that
> currently the quirks variable has very few statuses.
> 
> The rx_lvl_offset and tx_st_done store shift values, so that u8
> is a proper size.
> 
> fifo_lvl_mask stores a series of masks, to be in we will keep the
> 32 bit size.

What's the advantage of these changes?  This feels like microptimisation
of something that shouldn't be a big performance issue and it's not
always the case that the compiler does something more sensible with
smaller or unsigned types.  I'm not saying don't do it, I'm just saying
that it's not clear to me what the win is.

Andi Shyti July 5, 2016, 3:01 p.m. UTC | #2

Hi Mark,

> > The 'quirks' variable cannot ever be negative, therefore use u8
> > instead of int. The 8 bit size is given from the fact that
> > currently the quirks variable has very few statuses.
> > 
> > The rx_lvl_offset and tx_st_done store shift values, so that u8
> > is a proper size.
> > 
> > fifo_lvl_mask stores a series of masks, to be in we will keep the
> > 32 bit size.
> 
> What's the advantage of these changes?  This feels like microptimisation
> of something that shouldn't be a big performance issue and it's not
> always the case that the compiler does something more sensible with
> smaller or unsigned types.  I'm not saying don't do it, I'm just saying
> that it's not clear to me what the win is.

not much indeed. Just something that was a little bothering me
while I was reading through.

Please, feel free to drop it.

Thanks,
Andi

Patch

diff --git a/drivers/spi/spi-s3c64xx.c b/drivers/spi/spi-s3c64xx.c
index 6d8486f..6c9503a 100644
--- a/drivers/spi/spi-s3c64xx.c
+++ b/drivers/spi/spi-s3c64xx.c
@@ -150,10 +150,10 @@  struct s3c64xx_spi_dma_data {
  * which is provided as driver data to the driver.
  */
 struct s3c64xx_spi_port_config {
-	int	fifo_lvl_mask[MAX_SPI_PORTS];
-	int	rx_lvl_offset;
-	int	tx_st_done;
-	int	quirks;
+	u32	fifo_lvl_mask[MAX_SPI_PORTS];
+	u8	rx_lvl_offset;
+	u8	tx_st_done;
+	u8	quirks;
 	bool	high_speed;
 	bool	clk_from_cmu;
 };