[PATCH 0/9] Enable dw-mmc multi-card support

[PATCH 0/9] Enable dw-mmc multi-card support

[Liming Sun]

This series of commits enables the multi-card support for the dw-mmc
controller. It includes two parts as below.

The first part (patches 1-7) reverts the series of recent commits that
removed the multi-card support with comments saying there was no such
use case in the real world. Actually this feature is being used in
Mellanox Bluefield SoC and has been requested by customers.

The second part (patches 8-9) fixes the DesignWare multi-card support
according to the dw-mmc databook (synnopsys: DesignWare Cores Mobile
Storage Host Databook, 2.70a). It has changes to set the card number
into the CMD register to multiplex requests to different cards when
working in SD_MMC_CEATA mode, set the CTYPE / CLKENA / CDTHRCTL
registers properly according to the spec, and parse the per-card
configuration to match the Linux Documentation
(bindings/mmc/synopsys-dw-mshc.txt).

Liming Sun (9):
  Revert "Documentation: dw-mshc: deprecate num-slots"
  Revert "mmc: dw_mmc: remove the unnecessary slot variable"
  Revert "mmc: dw_mmc: use the 'slot' instead of 'cur_slot'"
  Revert "mmc: dw_mmc: remove the 'id' arguments about functions
    relevant to slot"
  Revert "mmc: dw_mmc: change the array of slots"
  Revert "mmc: dw_mmc: remove the loop about finding slots"
  Revert "mmc: dw_mmc: deprecated the "num-slots" property"
  mmc: dw_mmc: Support two SD_MMC_CE-ATA cards
  mmc: dw_mmc: Parse slot-specific configuration

 .../devicetree/bindings/mmc/synopsys-dw-mshc.txt   |  16 +-
 drivers/mmc/host/dw_mmc-exynos.c                   |   4 +-
 drivers/mmc/host/dw_mmc.c                          | 277 ++++++++++++++++-----
 drivers/mmc/host/dw_mmc.h                          |  17 +-
 4 files changed, 236 insertions(+), 78 deletions(-)

-- 
1.8.3.1

[PATCH 1/9] Revert "Documentation: dw-mshc: deprecate num-slots"

[Liming Sun]

This reverts commit 3f5b4b79d4c0fa71fd7d74c2a44bbc0869c04c9b.

The Mellanox BlueField SoC requires multiple slot dw-mmc support.

Signed-off-by: Liming Sun <lsun@mellanox.com>
---
 .../devicetree/bindings/mmc/synopsys-dw-mshc.txt         | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/Documentation/devicetree/bindings/mmc/synopsys-dw-mshc.txt b/Documentation/devicetree/bindings/mmc/synopsys-dw-mshc.txt
index ef3e5f1..9cb55ca 100644
--- a/Documentation/devicetree/bindings/mmc/synopsys-dw-mshc.txt
+++ b/Documentation/devicetree/bindings/mmc/synopsys-dw-mshc.txt
@@ -12,12 +12,12 @@ Required Properties:
 * #address-cells: should be 1.
 * #size-cells: should be 0.
 
-# Slots (DEPRECATED): The slot specific information are contained within
-  child-nodes with each child-node representing a supported slot. There should
-  be atleast one child node representing a card slot. The name of the child node
-  representing the slot is recommended to be slot@n where n is the unique number
-  of the slot connected to the controller. The following are optional properties
-  which can be included in the slot child node.
+# Slots: The slot specific information are contained within child-nodes with
+  each child-node representing a supported slot. There should be atleast one
+  child node representing a card slot. The name of the child node representing
+  the slot is recommended to be slot@n where n is the unique number of the slot
+  connected to the controller. The following are optional properties which
+  can be included in the slot child node.
 
 	* reg: specifies the physical slot number. The valid values of this
 	  property is 0 to (num-slots -1), where num-slots is the value
@@ -63,7 +63,7 @@ Optional properties:
   clock(cclk_out). If it's not specified, max is 200MHZ and min is 400KHz by default.
 	  (Use the "max-frequency" instead of "clock-freq-min-max".)
 
-* num-slots (DEPRECATED): specifies the number of slots supported by the controller.
+* num-slots: specifies the number of slots supported by the controller.
   The number of physical slots actually used could be equal or less than the
   value specified by num-slots. If this property is not specified, the value
   of num-slot property is assumed to be 1.
@@ -124,6 +124,7 @@ board specific portions as listed below.
 	dwmmc0@12200000 {
 		clock-frequency = <400000000>;
 		clock-freq-min-max = <400000 200000000>;
+		num-slots = <1>;
 		broken-cd;
 		fifo-depth = <0x80>;
 		card-detect-delay = <200>;
@@ -138,6 +139,7 @@ board specific portions as listed below.
 	dwmmc0@12200000 {
 		clock-frequency = <400000000>;
 		clock-freq-min-max = <400000 200000000>;
+		num-slots = <1>;
 		broken-cd;
 		fifo-depth = <0x80>;
 		card-detect-delay = <200>;
-- 
1.8.3.1

Re: [PATCH 1/9] Revert "Documentation: dw-mshc: deprecate num-slots"

[Rob Herring]

On Fri, Oct 06, 2017 at 03:21:24PM -0400, Liming Sun wrote:
> This reverts commit 3f5b4b79d4c0fa71fd7d74c2a44bbc0869c04c9b.
> 
> The Mellanox BlueField SoC requires multiple slot dw-mmc support.
> 
> Signed-off-by: Liming Sun <lsun@mellanox.com>
> ---
>  .../devicetree/bindings/mmc/synopsys-dw-mshc.txt         | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)

Acked-by: Rob Herring <robh@kernel.org>

RE: [PATCH 0/9] Enable dw-mmc multi-card support

[Liming Sun]

So far I saw one comment (an ACK) on PATCH 1/9. There seems no comments on other patches yet. 
Ulf, (or other maintainers), any comments or suggestions how to move forward for this patch series?

Thanks,
Liming

-----Original Message-----
From: linux-kernel-owner@vger.kernel.org [mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of Liming Sun
Sent: Friday, October 6, 2017 3:21 PM
To: Ulf Hansson <ulf.hansson@linaro.org>; Rob Herring <robh+dt@kernel.org>; Mark Rutland <mark.rutland@arm.com>; Jaehoon Chung <jh80.chung@samsung.com>; Kukjin Kim <kgene@kernel.org>; Krzysztof Kozlowski <krzk@kernel.org>
Cc: Liming Sun <lsun@mellanox.com>; linux-mmc@vger.kernel.org; devicetree@vger.kernel.org; linux-kernel@vger.kernel.org; linux-arm-kernel@lists.infradead.org; linux-samsung-soc@vger.kernel.org
Subject: [PATCH 0/9] Enable dw-mmc multi-card support

This series of commits enables the multi-card support for the dw-mmc controller. It includes two parts as below.

The first part (patches 1-7) reverts the series of recent commits that removed the multi-card support with comments saying there was no such use case in the real world. Actually this feature is being used in Mellanox Bluefield SoC and has been requested by customers.

The second part (patches 8-9) fixes the DesignWare multi-card support according to the dw-mmc databook (synnopsys: DesignWare Cores Mobile Storage Host Databook, 2.70a). It has changes to set the card number into the CMD register to multiplex requests to different cards when working in SD_MMC_CEATA mode, set the CTYPE / CLKENA / CDTHRCTL registers properly according to the spec, and parse the per-card configuration to match the Linux Documentation (bindings/mmc/synopsys-dw-mshc.txt).

Liming Sun (9):
  Revert "Documentation: dw-mshc: deprecate num-slots"
  Revert "mmc: dw_mmc: remove the unnecessary slot variable"
  Revert "mmc: dw_mmc: use the 'slot' instead of 'cur_slot'"
  Revert "mmc: dw_mmc: remove the 'id' arguments about functions
    relevant to slot"
  Revert "mmc: dw_mmc: change the array of slots"
  Revert "mmc: dw_mmc: remove the loop about finding slots"
  Revert "mmc: dw_mmc: deprecated the "num-slots" property"
  mmc: dw_mmc: Support two SD_MMC_CE-ATA cards
  mmc: dw_mmc: Parse slot-specific configuration

 .../devicetree/bindings/mmc/synopsys-dw-mshc.txt   |  16 +-
 drivers/mmc/host/dw_mmc-exynos.c                   |   4 +-
 drivers/mmc/host/dw_mmc.c                          | 277 ++++++++++++++++-----
 drivers/mmc/host/dw_mmc.h                          |  17 +-
 4 files changed, 236 insertions(+), 78 deletions(-)

--
1.8.3.1

Re: [PATCH 0/9] Enable dw-mmc multi-card support

[Shawn Lin]

On 2017/10/7 3:21, Liming Sun wrote:
> This series of commits enables the multi-card support for the dw-mmc
> controller. It includes two parts as below.
> 
> The first part (patches 1-7) reverts the series of recent commits that
> removed the multi-card support with comments saying there was no such
> use case in the real world. Actually this feature is being used in
> Mellanox Bluefield SoC and has been requested by customers.

Hrm.... it's so unlucky that your patchset comes a little late. As
your patch 8 and 9 said, you need them to fix problem for multi-card
support, so definitely there was no such use case, and even the code
was buggy to support it right? That makes the code hard to read and
maintain, so we decide to remove it.

> 
> The second part (patches 8-9) fixes the DesignWare multi-card support
> according to the dw-mmc databook (synnopsys: DesignWare Cores Mobile
> Storage Host Databook, 2.70a). It has changes to set the card number
> into the CMD register to multiplex requests to different cards when
> working in SD_MMC_CEATA mode, set the CTYPE / CLKENA / CDTHRCTL
> registers properly according to the spec, and parse the per-card
> configuration to match the Linux Documentation
> (bindings/mmc/synopsys-dw-mshc.txt).

Havn'e check the databook for details yet, but I think it's ok
to re-introduce multi-slot support if a real user benefits from
it. But you need a new patch to silent the log "num-slots property not
found, assuming 1 slot is available" as we removed all the num-slots
from DT at that time.


> 
> Liming Sun (9):
>    Revert "Documentation: dw-mshc: deprecate num-slots"
>    Revert "mmc: dw_mmc: remove the unnecessary slot variable"
>    Revert "mmc: dw_mmc: use the 'slot' instead of 'cur_slot'"
>    Revert "mmc: dw_mmc: remove the 'id' arguments about functions
>      relevant to slot"
>    Revert "mmc: dw_mmc: change the array of slots"
>    Revert "mmc: dw_mmc: remove the loop about finding slots"
>    Revert "mmc: dw_mmc: deprecated the "num-slots" property"
>    mmc: dw_mmc: Support two SD_MMC_CE-ATA cards
>    mmc: dw_mmc: Parse slot-specific configuration
> 
>   .../devicetree/bindings/mmc/synopsys-dw-mshc.txt   |  16 +-
>   drivers/mmc/host/dw_mmc-exynos.c                   |   4 +-
>   drivers/mmc/host/dw_mmc.c                          | 277 ++++++++++++++++-----
>   drivers/mmc/host/dw_mmc.h                          |  17 +-
>   4 files changed, 236 insertions(+), 78 deletions(-)
> 

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RE: [PATCH 0/9] Enable dw-mmc multi-card support

[Liming Sun]

>> Hrm.... it's so unlucky that your patchset comes a little late. As your patch 8 and 9 said, you need them to fix problem for multi-card support, so definitely there was no such use case, and even the code was buggy to support it right? That makes the code hard to read and maintain, so we decide to remove it.

Thanks for the feedback. Yes, earlier the multi-card support was buggy indeed. We spent some time to debug it and got it working.

>> Havn'e check the databook for details yet, but I think it's ok to re-introduce multi-slot support if a real user benefits from it. But you need a new patch to silent the log "num-slots property not found, assuming 1 slot is available" as we removed all the num-slots from DT at that time.

The " num-slots property not found..." log message has already been removed by 8a629d26f back in 2016. Looks like we're good on this one. In dw_mci_probe (), it has code to check pdata->num_slots. If 0, the host->num_slots will be set to 1. So the logic of setting default num_slots seems already there. But correct me if I am wrong.

Thanks,
Liming

-----Original Message-----
From: Shawn Lin [mailto:shawn.lin@rock-chips.com] 
Sent: Monday, October 16, 2017 9:36 PM
To: Liming Sun <lsun@mellanox.com>; Jaehoon Chung <jh80.chung@samsung.com>
Cc: Ulf Hansson <ulf.hansson@linaro.org>; Rob Herring <robh+dt@kernel.org>; Mark Rutland <mark.rutland@arm.com>; Kukjin Kim <kgene@kernel.org>; Krzysztof Kozlowski <krzk@kernel.org>; shawn.lin@rock-chips.com; linux-mmc@vger.kernel.org; devicetree@vger.kernel.org; linux-kernel@vger.kernel.org; linux-arm-kernel@lists.infradead.org; linux-samsung-soc@vger.kernel.org
Subject: Re: [PATCH 0/9] Enable dw-mmc multi-card support


On 2017/10/7 3:21, Liming Sun wrote:
> This series of commits enables the multi-card support for the dw-mmc 
> controller. It includes two parts as below.
> 
> The first part (patches 1-7) reverts the series of recent commits that 
> removed the multi-card support with comments saying there was no such 
> use case in the real world. Actually this feature is being used in 
> Mellanox Bluefield SoC and has been requested by customers.

Hrm.... it's so unlucky that your patchset comes a little late. As your patch 8 and 9 said, you need them to fix problem for multi-card support, so definitely there was no such use case, and even the code was buggy to support it right? That makes the code hard to read and maintain, so we decide to remove it.

> 
> The second part (patches 8-9) fixes the DesignWare multi-card support 
> according to the dw-mmc databook (synnopsys: DesignWare Cores Mobile 
> Storage Host Databook, 2.70a). It has changes to set the card number 
> into the CMD register to multiplex requests to different cards when 
> working in SD_MMC_CEATA mode, set the CTYPE / CLKENA / CDTHRCTL 
> registers properly according to the spec, and parse the per-card 
> configuration to match the Linux Documentation 
> (bindings/mmc/synopsys-dw-mshc.txt).

Havn'e check the databook for details yet, but I think it's ok to re-introduce multi-slot support if a real user benefits from it. But you need a new patch to silent the log "num-slots property not found, assuming 1 slot is available" as we removed all the num-slots from DT at that time.


> 
> Liming Sun (9):
>    Revert "Documentation: dw-mshc: deprecate num-slots"
>    Revert "mmc: dw_mmc: remove the unnecessary slot variable"
>    Revert "mmc: dw_mmc: use the 'slot' instead of 'cur_slot'"
>    Revert "mmc: dw_mmc: remove the 'id' arguments about functions
>      relevant to slot"
>    Revert "mmc: dw_mmc: change the array of slots"
>    Revert "mmc: dw_mmc: remove the loop about finding slots"
>    Revert "mmc: dw_mmc: deprecated the "num-slots" property"
>    mmc: dw_mmc: Support two SD_MMC_CE-ATA cards
>    mmc: dw_mmc: Parse slot-specific configuration
> 
>   .../devicetree/bindings/mmc/synopsys-dw-mshc.txt   |  16 +-
>   drivers/mmc/host/dw_mmc-exynos.c                   |   4 +-
>   drivers/mmc/host/dw_mmc.c                          | 277 ++++++++++++++++-----
>   drivers/mmc/host/dw_mmc.h                          |  17 +-
>   4 files changed, 236 insertions(+), 78 deletions(-)
> 

Re: [PATCH 0/9] Enable dw-mmc multi-card support

[Jaehoon Chung]

Sorry for late this..

On 10/18/2017 12:52 AM, Liming Sun wrote:
>>> Hrm.... it's so unlucky that your patchset comes a little late. As your patch 8 and 9 said, you need them to fix problem for multi-card support, so definitely there was no such use case, and even the code was buggy to support it right? That makes the code hard to read and maintain, so we decide to remove it.
> 
> Thanks for the feedback. Yes, earlier the multi-card support was buggy indeed. We spent some time to debug it and got it working.
> 
>>> Havn'e check the databook for details yet, but I think it's ok to re-introduce multi-slot support if a real user benefits from it. But you need a new patch to silent the log "num-slots property not found, assuming 1 slot is available" as we removed all the num-slots from DT at that time.
> 
> The " num-slots property not found..." log message has already been removed by 8a629d26f back in 2016. Looks like we're good on this one. In dw_mci_probe (), it has code to check pdata->num_slots. If 0, the host->num_slots will be set to 1. So the logic of setting default num_slots seems already there. But correct me if I am wrong.
> 
> Thanks,
> Liming
> 
> -----Original Message-----
> From: Shawn Lin [mailto:shawn.lin@rock-chips.com] 
> Sent: Monday, October 16, 2017 9:36 PM
> To: Liming Sun <lsun@mellanox.com>; Jaehoon Chung <jh80.chung@samsung.com>
> Cc: Ulf Hansson <ulf.hansson@linaro.org>; Rob Herring <robh+dt@kernel.org>; Mark Rutland <mark.rutland@arm.com>; Kukjin Kim <kgene@kernel.org>; Krzysztof Kozlowski <krzk@kernel.org>; shawn.lin@rock-chips.com; linux-mmc@vger.kernel.org; devicetree@vger.kernel.org; linux-kernel@vger.kernel.org; linux-arm-kernel@lists.infradead.org; linux-samsung-soc@vger.kernel.org
> Subject: Re: [PATCH 0/9] Enable dw-mmc multi-card support
> 
> 
> On 2017/10/7 3:21, Liming Sun wrote:
>> This series of commits enables the multi-card support for the dw-mmc 
>> controller. It includes two parts as below.
>>
>> The first part (patches 1-7) reverts the series of recent commits that 
>> removed the multi-card support with comments saying there was no such 
>> use case in the real world. Actually this feature is being used in 
>> Mellanox Bluefield SoC and has been requested by customers.
> 
> Hrm.... it's so unlucky that your patchset comes a little late. As your patch 8 and 9 said, you need them to fix problem for multi-card support, so definitely there was no such use case, and even the code was buggy to support it right? That makes the code hard to read and maintain, so we decide to remove it.

Hmm..
Well, if i missed your reply for my removing patch, it's my fault..but i didn't see any reply..
At that time, we didn't see any usage and also now...

Are there any patches for using multi slot? 
e,g) device-tree file or your own driver

If there are big benefits to revert them,  i don't want to back them..during almost 6 years, never use it..

> 
>>
>> The second part (patches 8-9) fixes the DesignWare multi-card support 
>> according to the dw-mmc databook (synnopsys: DesignWare Cores Mobile 
>> Storage Host Databook, 2.70a). It has changes to set the card number 
>> into the CMD register to multiplex requests to different cards when 
>> working in SD_MMC_CEATA mode, set the CTYPE / CLKENA / CDTHRCTL 
>> registers properly according to the spec, and parse the per-card 
>> configuration to match the Linux Documentation 
>> (bindings/mmc/synopsys-dw-mshc.txt).

the second part seems that it's only support since v2.70a..?

> 
> Havn'e check the databook for details yet, but I think it's ok to re-introduce multi-slot support if a real user benefits from it. But you need a new patch to silent the log "num-slots property not found, assuming 1 slot is available" as we removed all the num-slots from DT at that time.
> 
> 
>>
>> Liming Sun (9):
>>    Revert "Documentation: dw-mshc: deprecate num-slots"
>>    Revert "mmc: dw_mmc: remove the unnecessary slot variable"
>>    Revert "mmc: dw_mmc: use the 'slot' instead of 'cur_slot'"
>>    Revert "mmc: dw_mmc: remove the 'id' arguments about functions
>>      relevant to slot"
>>    Revert "mmc: dw_mmc: change the array of slots"
>>    Revert "mmc: dw_mmc: remove the loop about finding slots"
>>    Revert "mmc: dw_mmc: deprecated the "num-slots" property"
>>    mmc: dw_mmc: Support two SD_MMC_CE-ATA cards
>>    mmc: dw_mmc: Parse slot-specific configuration
>>
>>   .../devicetree/bindings/mmc/synopsys-dw-mshc.txt   |  16 +-
>>   drivers/mmc/host/dw_mmc-exynos.c                   |   4 +-
>>   drivers/mmc/host/dw_mmc.c                          | 277 ++++++++++++++++-----
>>   drivers/mmc/host/dw_mmc.h                          |  17 +-
>>   4 files changed, 236 insertions(+), 78 deletions(-)
>>
> 
> 
> 
> 

RE: [PATCH 0/9] Enable dw-mmc multi-card support

[Liming Sun]

Thanks Jaehoon. Please also see my response inline.

- Liming

> -----Original Message-----
> From: Jaehoon Chung [mailto:jh80.chung@samsung.com]
> Sent: Friday, October 20, 2017 10:06 AM
> To: Liming Sun <lsun@mellanox.com>; Shawn Lin <shawn.lin@rock-
> chips.com>
> Cc: Ulf Hansson <ulf.hansson@linaro.org>; Rob Herring
> <robh+dt@kernel.org>; Mark Rutland <mark.rutland@arm.com>; Kukjin Kim
> <kgene@kernel.org>; Krzysztof Kozlowski <krzk@kernel.org>; linux-
> mmc@vger.kernel.org; devicetree@vger.kernel.org; linux-
> kernel@vger.kernel.org; linux-arm-kernel@lists.infradead.org; linux-
> samsung-soc@vger.kernel.org; Chris Metcalf <cmetcalf@mellanox.com>
> Subject: Re: [PATCH 0/9] Enable dw-mmc multi-card support
> 
> Sorry for late this..
> 
> On 10/18/2017 12:52 AM, Liming Sun wrote:
> >>> Hrm.... it's so unlucky that your patchset comes a little late. As your patch
> 8 and 9 said, you need them to fix problem for multi-card support, so
> definitely there was no such use case, and even the code was buggy to
> support it right? That makes the code hard to read and maintain, so we
> decide to remove it.
> >
> > Thanks for the feedback. Yes, earlier the multi-card support was buggy
> indeed. We spent some time to debug it and got it working.
> >
> >>> Havn'e check the databook for details yet, but I think it's ok to re-
> introduce multi-slot support if a real user benefits from it. But you need a
> new patch to silent the log "num-slots property not found, assuming 1 slot is
> available" as we removed all the num-slots from DT at that time.
> >
> > The " num-slots property not found..." log message has already been
> removed by 8a629d26f back in 2016. Looks like we're good on this one. In
> dw_mci_probe (), it has code to check pdata->num_slots. If 0, the host-
> >num_slots will be set to 1. So the logic of setting default num_slots seems
> already there. But correct me if I am wrong.
> >
> > Thanks,
> > Liming
> >
> > -----Original Message-----
> > From: Shawn Lin [mailto:shawn.lin@rock-chips.com]
> > Sent: Monday, October 16, 2017 9:36 PM
> > To: Liming Sun <lsun@mellanox.com>; Jaehoon Chung
> > <jh80.chung@samsung.com>
> > Cc: Ulf Hansson <ulf.hansson@linaro.org>; Rob Herring
> > <robh+dt@kernel.org>; Mark Rutland <mark.rutland@arm.com>; Kukjin
> Kim
> > <kgene@kernel.org>; Krzysztof Kozlowski <krzk@kernel.org>;
> > shawn.lin@rock-chips.com; linux-mmc@vger.kernel.org;
> > devicetree@vger.kernel.org; linux-kernel@vger.kernel.org;
> > linux-arm-kernel@lists.infradead.org;
> > linux-samsung-soc@vger.kernel.org
> > Subject: Re: [PATCH 0/9] Enable dw-mmc multi-card support
> >
> >
> > On 2017/10/7 3:21, Liming Sun wrote:
> >> This series of commits enables the multi-card support for the dw-mmc
> >> controller. It includes two parts as below.
> >>
> >> The first part (patches 1-7) reverts the series of recent commits
> >> that removed the multi-card support with comments saying there was no
> >> such use case in the real world. Actually this feature is being used
> >> in Mellanox Bluefield SoC and has been requested by customers.
> >
> > Hrm.... it's so unlucky that your patchset comes a little late. As your patch 8
> and 9 said, you need them to fix problem for multi-card support, so definitely
> there was no such use case, and even the code was buggy to support it right?
> That makes the code hard to read and maintain, so we decide to remove it.
> 
> Hmm..
> Well, if i missed your reply for my removing patch, it's my fault..but i didn't
> see any reply..
> At that time, we didn't see any usage and also now...

[Liming] It is definitely not anybody's fault. My apology that I should have made it very clear.
This is a new SoC which uses two eMMC cards. This feature has been requested by customer.
We made it working with patches, then realized that the support for the 2nd card was removed recently from upstream kernel.
To avoid reinventing the wheel, a better approach appears to bring back the changes.

> 
> Are there any patches for using multi slot?
> e,g) device-tree file or your own driver

[Liming] Patch 9/8 and 9/9 are the changes to fix the multi-slot support.
We follow the original "Documentation/devicetree/bindings/mmc/synopsys-dw-mshc.txt" for device configuration.
There is no device-tree patches since there is no changes to any of the documentation syntax.

Just in case you might be interested, below is the ACPI table we used to include the two slots. It's defined according to synopsys-dw-mshc.txt and seems working.

    Device (MMC0) {
      Name (_HID, "PRP0001")
      Name (_UID, Zero)
      Name (_CCA, 1)
      Name (_CRS, ResourceTemplate() {
        Memory32Fixed(ReadWrite, 0x6008000, 0x400)
        Interrupt(ResourceConsumer, Level, ActiveHigh, Exclusive) { 64 }
      })

      // Common configuration
      Name(_DSD, Package() {
        ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
        Package() {
          Package () { "compatible", Package () {"snps,dw-mshc"}},
          Package () { "fifo-depth", 0x100 },
          Package () { "clock-frequency", 24000000 },
          Package () { "cap-mmc-highspeed", 1 },
          Package () { "card-detect-delay", 200 },
          Package () { "num-slots", 2 }
        }
      })

      // Slot-0
      Device (SLT0) {
        Name(_DSD, Package() {
          ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
          Package() {
            Package () { "reg", 0 },              // physical slot number
            Package () { "bus-width", 8 }         // bus width (8-bit)
          }
        })
      }

      // Slot-1
      Device (SLT1) {
        Name(_DSD, Package() {
          ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
          Package() {
            Package () { "reg", 1 },              // physical slot number
            Package () { "bus-width", 4 }         // bus width (4-bit)
          }
        })
      }
    }
> 
> If there are big benefits to revert them,  i don't want to back them..during
> almost 6 years, never use it..

[Liming] Yeah, I could imagine it. Earlier the multi-slot didn't work well at all.
We debug it on HW emulation to figure it out. The changes are not big though. 
We have customers asking for it. It'll be very helpful to re-enable the multi-card support.

> 
> >
> >>
> >> The second part (patches 8-9) fixes the DesignWare multi-card support
> >> according to the dw-mmc databook (synnopsys: DesignWare Cores
> Mobile
> >> Storage Host Databook, 2.70a). It has changes to set the card number
> >> into the CMD register to multiplex requests to different cards when
> >> working in SD_MMC_CEATA mode, set the CTYPE / CLKENA / CDTHRCTL
> >> registers properly according to the spec, and parse the per-card
> >> configuration to match the Linux Documentation
> >> (bindings/mmc/synopsys-dw-mshc.txt).
> 
> the second part seems that it's only support since v2.70a..?

[Liming] This one is the spec I used as reference for all the changes and testing.
I didn't go through previous versions due to the limitation of testing environment I have.
As you mentioned, there is no multi-card usage earlier and this SoC is probably the first
product to use it in real-world. So adding a version check seems safe (so it won't
unnecessarily break anything just in case) . Any suggestions?

> 
> >
> > Havn'e check the databook for details yet, but I think it's ok to re-introduce
> multi-slot support if a real user benefits from it. But you need a new patch to
> silent the log "num-slots property not found, assuming 1 slot is available" as
> we removed all the num-slots from DT at that time.
> >
> >
> >>
> >> Liming Sun (9):
> >>    Revert "Documentation: dw-mshc: deprecate num-slots"
> >>    Revert "mmc: dw_mmc: remove the unnecessary slot variable"
> >>    Revert "mmc: dw_mmc: use the 'slot' instead of 'cur_slot'"
> >>    Revert "mmc: dw_mmc: remove the 'id' arguments about functions
> >>      relevant to slot"
> >>    Revert "mmc: dw_mmc: change the array of slots"
> >>    Revert "mmc: dw_mmc: remove the loop about finding slots"
> >>    Revert "mmc: dw_mmc: deprecated the "num-slots" property"
> >>    mmc: dw_mmc: Support two SD_MMC_CE-ATA cards
> >>    mmc: dw_mmc: Parse slot-specific configuration
> >>
> >>   .../devicetree/bindings/mmc/synopsys-dw-mshc.txt   |  16 +-
> >>   drivers/mmc/host/dw_mmc-exynos.c                   |   4 +-
> >>   drivers/mmc/host/dw_mmc.c                          | 277 ++++++++++++++++----
> -
> >>   drivers/mmc/host/dw_mmc.h                          |  17 +-
> >>   4 files changed, 236 insertions(+), 78 deletions(-)
> >>
> >
> >
> >
> >

Re: [PATCH 0/9] Enable dw-mmc multi-card support

[Ulf Hansson]

Hi Liming,

Sorry for jumping into the discussion like this.

[...]

>> >> This series of commits enables the multi-card support for the dw-mmc
>> >> controller. It includes two parts as below.
>> >>
>> >> The first part (patches 1-7) reverts the series of recent commits
>> >> that removed the multi-card support with comments saying there was no
>> >> such use case in the real world. Actually this feature is being used
>> >> in Mellanox Bluefield SoC and has been requested by customers.
>> >
>> > Hrm.... it's so unlucky that your patchset comes a little late. As your patch 8
>> and 9 said, you need them to fix problem for multi-card support, so definitely
>> there was no such use case, and even the code was buggy to support it right?
>> That makes the code hard to read and maintain, so we decide to remove it.

Unfortunate patch 8 and 9 does *not* solve the fundamental problem
with multiple slots. You can't solve it without involving the mmc
core, as explained in earlier discussions [1].

>>
>> Hmm..
>> Well, if i missed your reply for my removing patch, it's my fault..but i didn't
>> see any reply..
>> At that time, we didn't see any usage and also now...
>
> [Liming] It is definitely not anybody's fault. My apology that I should have made it very clear.
> This is a new SoC which uses two eMMC cards. This feature has been requested by customer.
> We made it working with patches, then realized that the support for the 2nd card was removed recently from upstream kernel.
> To avoid reinventing the wheel, a better approach appears to bring back the changes.
>
>>

Having multiple slots of eMMC:s, attached to one single mmc
controller, is really a terrible idea, even if one could get it to
somewhat work.

To deal with multiple slots from the mmc core point of view, we would
need to introduce  a kind of "bus slot lock", which needs to be taken
whenever the core access any of the registered two mmc hosts.

However, that then means that the upper block device layers can no
longer perform proper I/O scheduling of requests to the eMMC cards. In
other words, requests on one eMMC device can then starve requests
reaching the other eMMC device. It all falls apart.

Perhaps that is a limitation you think is okay to live with, but I am
really not so sure it's worth adding "multiple slot" support.

[...]

Kind regards
Uffe

Re: [PATCH 0/9] Enable dw-mmc multi-card support

[Ulf Hansson]

[...]

> Unfortunate patch 8 and 9 does *not* solve the fundamental problem
> with multiple slots. You can't solve it without involving the mmc
> core, as explained in earlier discussions [1].
>

This link got lost, so here it is:

[1]
https://www.spinics.net/lists/linux-mmc/msg46549.html

[...]

Kind regards
Uffe