Re: [Linux-stm32] [PATCH V3 1/3] mmc: mmci: fix read status for busy detect

From: Ludovic BARRE
Date: Mon Aug 05 2019 - 03:33:44 EST

hi Ulf

On 7/26/19 11:41 AM, Ludovic BARRE wrote:
hi Ulf

Thanks to your "Clarify comments ..." commit, like is closes
I resumed upstream of this series.

On 7/15/19 6:31 PM, Ulf Hansson wrote:
On Mon, 3 Jun 2019 at 17:55, Ludovic Barre <ludovic.Barre@xxxxxx> wrote:

From: Ludovic Barre <ludovic.barre@xxxxxx>

"busy_detect_flag" is used to read & clear busy value of mmci status.
"busy_detect_mask" is used to manage busy irq of mmci mask.
So to read mmci status the busy_detect_flag must be take account.
if the variant does not support busy detect feature the flag is null
and there is no impact.

By reading the changelog, it doesn't tell me the purpose of this
change. When going forward, please work harder on your changelogs.

Make sure to answer the questions, *why* is this change needed,
*what/how* does the change do.

Ok, I will explain the differences with the legacy and the needs of sdmmc variant about busy detection.

Not need to re-read the status register in mmci_cmd_irq, the
status parameter can be used.

Signed-off-by: Ludovic Barre <ludovic.barre@xxxxxx>
 drivers/mmc/host/mmci.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/mmc/host/mmci.c b/drivers/mmc/host/mmci.c
index 356833a..5b5cc45 100644
--- a/drivers/mmc/host/mmci.c
+++ b/drivers/mmc/host/mmci.c
@@ -1240,7 +1240,7 @@ mmci_cmd_irq(struct mmci_host *host, struct mmc_command *cmd,
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ if (!host->busy_status &&
-ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ (readl(base + MMCISTATUS) & host->variant->busy_detect_flag)) {
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ (status & host->variant->busy_detect_flag)) {

I suggested you to do this change through some of my earlier comments,
however I think it should be made as a stand alone change.

Anyway, when looking at the details in your series, I decided to try
to help out a bit, so I have prepared a couple of related patches for
cleaning up and clarifying the busy detection code/comments in mmci. I
have incorporated the above change, so let me post them asap.

ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ writel(host->variant->busy_detect_mask,
@@ -1517,7 +1517,8 @@ static irqreturn_t mmci_irq(int irq, void *dev_id)
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ * to make sure that both start and end interrupts are always
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ * cleared one after the other.
-ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ status &= readl(host->base + MMCIMASK0);
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ status &= readl(host->base + MMCIMASK0) |
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ host->variant->busy_detect_flag;

As I told earlier in the review, this looks wrong to me.

It means that you will add the bit for the ->busy_detect_flag to the
status field we have just read from the MMCISTATUS register. That
means the busy status may be set when it shouldn't.

ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ if (host->variant->busy_detect)
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ writel(status & ~host->variant->busy_detect_mask,

By looking at the other changes in the series, I assume @subject patch
is intended to prepare for the other changes on top. But it's not
really clear.

Anyway, in that regards, the below is my observations of what seems to
be important part, when supporting busy detection for the stm32 sdmmc
variant (except the timeout things in patch2, which I intend to
comment separately on).

I figured, these are the involved register bits/masks:



it's exact:
MCI_STM32_BUSYD0 BIT(20): This is a hardware status flag only (inverted value of d0 line), it does not generate an interrupt, and so no mask

MCI_STM32_BUSYD0ENDMASK BIT(21): This indicates only end of busy
following a CMD response. On busy to Not busy changes, an interrupt
is generated (if unmask) and BUSYD0END status flag is set.
status flag is cleared by writing corresponding interrupt clear bit in MMCICLEAR.

For the legacy ST variant, there is only one register bit in
MMCISTATUS that is used for indicating busy (MCI_ST_CARDBUSY BIT(24)).
There is no dedicated busy-end bit for the busy-end IRQ, which I
believe is the reason to why the current code also is bit messy.


It seems like the stm32 sdmmc variant have a separate status bit for
the busy-end IRQ, correct?


If I understand correctly by looking at patch3, you don't use the
dedicated busy-end status bit (MCI_STM32_BUSYD0END), right? Then why

like your are clarify in previous series, the busy detection is done
in 3 steps.

if I use:
.busy_detect_flagÂÂÂ = MCI_STM32_BUSYD0ENDMASK,
.busy_detect_maskÂÂÂ = MCI_STM32_BUSYD0ENDMASK,

the sdmmc request will be not correctly completed, because the third step can't be happen.

step1: when busyd0end change to 1
Â=> busyd0end interrupt is unmasked
Â=> busy_status = cmd_sent | respend
Â=> return to mmci_irq
step2: busyd0end is yet to 1
Â=> clear the busyd0end interrupt
ÂÂÂÂ=> the hardware clear busyd0end status flag on interrupt clear
Â=> return to mmci_irq

like MCI_STM32_BUSYD0END interrupt is generated only on change
busy to not busy, when the interrupt is cleared (status is 0)
the step 3 can't happen (no irq pending to re-enter in mmci_cmd_irq).
sdmmc can't complete the request.

If I use:
.busy_detect_flagÂÂÂ = MCI_STM32_BUSYD0,
.busy_detect_maskÂÂÂ = MCI_STM32_BUSYD0ENDMASK,

Like there is no MCI_STM32_BUSYD0 irq mask, the status read in mmci_irq
"status &= readl(host->base + MMCIMASK0)" can't take account the busy_detect_flag (for sdmmc). So the step 2 can't be passed.
However we could share re-read between step 1 and step 2.


+ÂÂÂÂÂÂÂ u32 busy_val = readl(base + MMCISTATUS) &
+ÂÂÂÂÂÂÂÂÂÂÂ host->variant->busy_detect_flag;
ÂÂÂÂÂÂÂÂ if (!host->busy_status &&
-ÂÂÂÂÂÂÂÂÂÂÂ (readl(base + MMCISTATUS) & host->variant->busy_detect_flag)) {

ÂÂÂÂÂÂÂÂÂÂÂÂ writel(readl(base + MMCIMASK0) |
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ host->variant->busy_detect_mask,
@@ -1262,8 +1265,7 @@ mmci_cmd_irq(struct mmci_host *host, struct mmc_command *cmd,
ÂÂÂÂÂÂÂÂÂ * both the start and the end interrupts needs to be cleared,
ÂÂÂÂÂÂÂÂÂ * one after the other. So, clear the busy start IRQ here.
-ÂÂÂÂÂÂÂ if (host->busy_status &&
-ÂÂÂÂÂÂÂÂÂÂÂ (status & host->variant->busy_detect_flag)) {
+ÂÂÂÂÂÂÂ if (host->busy_status && busy_val) {

what do you think about it ?

I give up this proposal for a new version based on mmci_host_ops
callback to done the busy completion.


Kind regards

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