Re: [RFC PATCH 2/2] mmc: dw_mmc: check card present before starting request

From: Shawn Lin
Date: Thu May 26 2016 - 22:27:13 EST


Hi Jaehoon,

On 2016/5/27 8:53, Jaehoon Chung wrote:
Hi Shawn,

On 05/26/2016 12:08 PM, Shawn Lin wrote:
The main reason to add this check is to avoid unnecessary
mmc_request if the card is removed. Although we have already
check this in dw_mci_handle_cd for runtime usage of sd card and
dw_mci_init_slot for noremovable devices, but there is a timing
gap before it really calls dw_mci_get_cd as mmc_detect_change needs
some delay here.

What's unnecessary mmc_request?

the on-going read/write/ and the corresponding sbc like cmd13, etc.




Another gain here is that we could save some checkings of card status
after sd card been removed.

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

drivers/mmc/host/dw_mmc.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
index cb30e91..2940d24 100644
--- a/drivers/mmc/host/dw_mmc.c
+++ b/drivers/mmc/host/dw_mmc.c
@@ -105,6 +105,7 @@ struct idmac_desc {
static bool dw_mci_reset(struct dw_mci *host);
static bool dw_mci_ctrl_reset(struct dw_mci *host, u32 reset);
static int dw_mci_card_busy(struct mmc_host *mmc);
+static int dw_mci_get_cd(struct mmc_host *mmc);

#if defined(CONFIG_DEBUG_FS)
static int dw_mci_req_show(struct seq_file *s, void *v)
@@ -1248,6 +1249,8 @@ static void dw_mci_request(struct mmc_host *mmc, struct mmc_request *mrq)

WARN_ON(slot->mrq);

+ dw_mci_get_cd(mmc);
+

If my understanding is right, it can be replaced

if (!test_bit(DW_MMC_CARD_PRESENT, &slot->flags))

to

if (!dw_mci_get_cd(mmc))

yeah~ It looks better.



Best Regards,
Jaehoon Chung



/*
* The check for card presence and queueing of the request must be
* atomic, otherwise the card could be removed in between and the







--
Best Regards
Shawn Lin