spi: dw: Fix detecting FIFO depth

AxelLin · broonie · commit d297933cc7fc · 2015-01-05T19:04:39.000Z
Current code tries to find the highest valid fifo depth by checking the value
it wrote to DW_SPI_TXFLTR. There are a few problems in current code:
1) There is an off-by-one in dws-&gt;fifo_len setting because it assumes the latest
   register write fails so the latest valid value should be fifo - 1.
2) We know the depth could be from 2 to 256 from HW spec, so it is not necessary
   to test fifo == 257. In the case fifo is 257, it means the latest valid
   setting is fifo = 256. So after the for loop iteration, we should check
   fifo == 2 case instead of fifo == 257 if detecting the FIFO depth fails.
This patch fixes above issues.

Signed-off-by: Axel Lin &lt;axel.lin@ingics.com&gt;
Reviewed-and-tested-by: Andy Shevchenko &lt;andriy.shevchenko@linux.intel.com&gt;
Signed-off-by: Mark Brown &lt;broonie@kernel.org&gt;
Cc: stable@vger.kernel.org
diff --git a/drivers/spi/spi-dw.c b/drivers/spi/spi-dw.c
@@ -621,13 +621,13 @@ static void spi_hw_init(struct dw_spi *dws)
 	if (!dws->fifo_len) {
 		u32 fifo;
 
-		for (fifo = 2; fifo <= 257; fifo++) {
+		for (fifo = 2; fifo <= 256; fifo++) {
 			dw_writew(dws, DW_SPI_TXFLTR, fifo);
 			if (fifo != dw_readw(dws, DW_SPI_TXFLTR))
 				break;
 		}
 
-		dws->fifo_len = (fifo == 257) ? 0 : fifo;
+		dws->fifo_len = (fifo == 2) ? 0 : fifo - 1;
 		dw_writew(dws, DW_SPI_TXFLTR, 0);
 	}
 }

Original file line number	Diff line number	Diff line change
`@@ -621,13 +621,13 @@ static void spi_hw_init(struct dw_spi *dws)`
`621`	`621`	`if (!dws->fifo_len) {`
`622`	`622`	`u32 fifo;`
`623`	`623`
`624`		`- for (fifo = 2; fifo <= 257; fifo++) {`
	`624`	`+ for (fifo = 2; fifo <= 256; fifo++) {`
`625`	`625`	`dw_writew(dws, DW_SPI_TXFLTR, fifo);`
`626`	`626`	`if (fifo != dw_readw(dws, DW_SPI_TXFLTR))`
`627`	`627`	`break;`
`628`	`628`	`}`
`629`	`629`
`630`		`- dws->fifo_len = (fifo == 257) ? 0 : fifo;`
	`630`	`+ dws->fifo_len = (fifo == 2) ? 0 : fifo - 1;`
`631`	`631`	`dw_writew(dws, DW_SPI_TXFLTR, 0);`
`632`	`632`	`}`
`633`	`633`	`}`