Re: [RFC PATCH] mmc: dw_mmc: remove redundant num_slots check

From: Shawn Lin
Date: Thu Jan 21 2016 - 22:07:41 EST

On 2016/1/22 10:46, Jaehoon Chung wrote:
Hi, Shawn.

On 01/21/2016 04:52 PM, Shawn Lin wrote:
num_slots comes from pdata if existing, otherwise from
dw_mci_parse_dt which make it at least one slot. If
num_slots is less than 1 for the existing pdata case,
current code return -ENODEV. But dw_mci_probe seems to
treat this a optional case as it will call SDMMC_GET_SLOT_NUM
if no slot assigned.

Well, we need to consider more thing..
Host can get the number of slot from SDMMC_GET_SLOT_NUM().
But i think this way also has the problem.

num_slot isn't defined anywhere, and num_slot should be set to value of SDMMC_GET_SLOT_NUM.
If that value is higher than 1, it should be blocking..(I didn't test all cases..)

Actually, from the code itself, it confused me the way about how we get
num_slot. At leaset, we might should try to cleanup it someway to make
it a little more clear. And just as what you point out, we see some
broblem here.

Even though this patch is not correct, i could check the problem relevant to num_slot, because of this patch. :)

Nice to here that. I make it a RFC patch since I also not quite sure
about all cases including some corner cases. Let's think it twice.

my suggestion is if pdata->num_slot is not defined anywhere, just set to 1 by default.
not take from SDMMC_GET_SLOT_NUM.

yes, SDMMC_GET_SLOT_NUM is the capability of controller, num_slot is
hardware wired number. So, geting it from SDMMC_GET_SLOT_NUM has

if (host->pdata->nums_slots < 1 ||
host->pdata->nums_slots > SDMMC_GET_SLOT_NUM())

This is correct condition. num_slots can't be higher than number of supported slots.
how about?

Seems reasonable.
I guess you want to come up with a new patch dealing with it? :)

Best Regards,
Jaehoon Chung

Signed-off-by: Shawn Lin <shawn.lin@xxxxxxxxxxxxxx>


drivers/mmc/host/dw_mmc.c | 6 ------
1 file changed, 6 deletions(-)

diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
index 7128351..a116ec6 100644
--- a/drivers/mmc/host/dw_mmc.c
+++ b/drivers/mmc/host/dw_mmc.c
@@ -2949,12 +2949,6 @@ int dw_mci_probe(struct dw_mci *host)

- if (host->pdata->num_slots < 1) {
- dev_err(host->dev,
- "Platform data must supply num_slots.\n");
- return -ENODEV;
- }
host->biu_clk = devm_clk_get(host->dev, "biu");
if (IS_ERR(host->biu_clk)) {
dev_dbg(host->dev, "biu clock not available\n");

Best Regards
Shawn Lin