[PATCH u-boot-spi v2 8/9] mtd: mtdpart: Make mtdpart's _erase method sane

["Marek Behún" <kabel@kernel.org>]

From: Marek Behún <marek.behun@nic.cz>

The _erase() method of the mtdpart driver, part_erase(), currently
implements offset shifting (for given mtdpart partition) in a weird way:
  1. part_erase() adds partition offset to block address
  2. parent driver's _erase() method is called
  3. parent driver's _erase() method calls mtd_erase_callback()
  4. mtd_erase_callback() subtracts partition offset from block address
     so that the callback function is given correct address
The problem here is that if the parent's driver does not call
mtd_erase_callback() in some scenario (this was recently a case for
spi_nor_erase(), which did not call mtd_erase_callback() at all), the
offset is not shifted back.

Moreover the code would be more readable if part_erase() not only added
partition offset before calling parent's _erase(), but also subtracted
it back afterwards. Currently the mtd_erase_callback() is expected to do
this subtracting since it does have to do it anyway.

Add the more steps to this procedure:
  5. mtd_erase_callback() adds partition offset to block address so that
     it returns the the erase_info structure members as it received them
  6. part_erase() subtracts partition offset from block address

This makes the code more logical and also prevents errors in case
parent's driver does not call mtd_erase_callback() for some reason.

(BTW, the purpose of mtd_erase_callback() in Linux is to inform the
 caller that it is done, since in Linux erasing is done asynchronously.
 We are abusing the purpose of mtd_erase_callback() in U-Boot for
 completely different purpose. The callback function itself has empty
 implementation in all cases in U-Boot.)

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Masami Hiramatsu <masami.hiramatsu@linaro.org>
---
 drivers/mtd/mtdpart.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/drivers/mtd/mtdpart.c b/drivers/mtd/mtdpart.c
index aa58f722da..6ab481a7b1 100644
--- a/drivers/mtd/mtdpart.c
+++ b/drivers/mtd/mtdpart.c
@@ -446,24 +446,34 @@ static int part_erase(struct mtd_info *mtd, struct erase_info *instr)
 	int ret;
 
 	instr->addr += mtd->offset;
+
 	ret = mtd->parent->_erase(mtd->parent, instr);
-	if (ret) {
-		if (instr->fail_addr != MTD_FAIL_ADDR_UNKNOWN)
-			instr->fail_addr -= mtd->offset;
-		instr->addr -= mtd->offset;
-	}
+	if (ret && instr->fail_addr != MTD_FAIL_ADDR_UNKNOWN)
+		instr->fail_addr -= mtd->offset;
+
+	instr->addr -= mtd->offset;
+
 	return ret;
 }
 
 void mtd_erase_callback(struct erase_info *instr)
 {
-	if (instr->mtd->_erase == part_erase) {
+	if (!instr->callback)
+		return;
+
+	if (instr->mtd->_erase == part_erase && instr->len) {
 		if (instr->fail_addr != MTD_FAIL_ADDR_UNKNOWN)
 			instr->fail_addr -= instr->mtd->offset;
 		instr->addr -= instr->mtd->offset;
 	}
-	if (instr->callback)
-		instr->callback(instr);
+
+	instr->callback(instr);
+
+	if (instr->mtd->_erase == part_erase && instr->len) {
+		if (instr->fail_addr != MTD_FAIL_ADDR_UNKNOWN)
+			instr->fail_addr += instr->mtd->offset;
+		instr->addr += instr->mtd->offset;
+	}
 }
 EXPORT_SYMBOL_GPL(mtd_erase_callback);
 
-- 
2.32.0