linux-kernel - RE: [PATCH V1 07/11] mmc: cqhci: add quirk for setting DCMD CMD

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Date:   Thu, 7 Mar 2019 18:16:08 +0000
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Ritesh Harjani <riteshh@...eaurora.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        "ulf.hansson@...aro.org" <ulf.hansson@...aro.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        Asutosh Das <asutoshd@...eaurora.org>
CC:     "thierry.reding@...il.com" <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Aniruddha Tvs Rao <anrao@...dia.com>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: RE: [PATCH V1 07/11] mmc: cqhci: add quirk for setting DCMD
 CMD_TIMING


> On 3/6/2019 6:30 PM, Adrian Hunter wrote:
>> On 2/03/19 7:20 AM, Sowjanya Komatineni wrote:
>>> This patch adds a quirk for setting CMD_TIMING to 1 in descriptor for 
>>> DCMD with R1B response type to allow the command to be sent to device 
>>> during data activity or busy time.
>>>
>>> Tegra186 CQHCI host has bug where it selects DATA_PRESENT_SELECT to 1 
>>> by CQHCI controller for DCMDs with R1B response type and since DCMD 
>>> does not trigger any data transfer, DCMD task complete happens 
>>> leaving the DATA FSM of host controller in wait state for data.
>>>
>>> This effects the data transfer task issued after R1B DCMD task and no 
>>> interrupt is generated for the data transfer task.
>>>
>>> SW WAR for this issue is to set CMD_TIMING bit to 1 in DCMD task 
>>> descriptor and as DCMD task descriptor preparation is done by cqhci 
>>> driver, this patch adds cqequirk to handle this.
>>>
>>> Signed-off-by: Sowjanya Komatineni <skomatineni@...dia.com>
>>> ---
>>>   drivers/mmc/host/cqhci.c | 5 ++++-
>>>   drivers/mmc/host/cqhci.h | 1 +
>>>   2 files changed, 5 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/mmc/host/cqhci.c b/drivers/mmc/host/cqhci.c 
>>> index a8af682a9182..b34c07125f32 100644
>>> --- a/drivers/mmc/host/cqhci.c
>>> +++ b/drivers/mmc/host/cqhci.c
>>> @@ -521,7 +521,10 @@ static void cqhci_prep_dcmd_desc(struct mmc_host *mmc,
>>>   	} else {
>>>   		if (mrq->cmd->flags & MMC_RSP_R1B) {
>>>   			resp_type = 0x3;
>>> -			timing = 0x0;
>>> +			if (cq_host->quirks & CQHCI_QUIRK_CMD_TIMING_R1B_DCMD)
>>> +				timing = 0x1;
>>> +			else
>>> +				timing = 0x0;
>> I was thinking it would be nice if there was a generic way for drivers 
>> to make changes to descriptors before a task is started.  Currently 
>> there is
>> host->ops->write_l() which would make it possible by checking for 
>> host->ops->CQHCI_TDBR
>> register and, in this case, the DCMD tag.  We would need to export 
>> get_desc(), perhaps rename it cqhci_get_desc() and put it in cqhci.h 
>> since it is an inline function.
>
>We take spin_lock_irqsave after the descriptor is prepared and before writing to TDBR.
>Not sure but tomorrow this may become a limitation for drivers to make changes to descriptors if they edit descriptors in host->ops->write_l() call.
>Though in this case it is not required here.
>
>>
>> Alternatively we could add host->ops for descriptor preparation.
>
>Both ways sounds good to me.
>But maybe adding a host->ops for descriptor preparation is better way to go,
>since that will be the right interface exposed to make changes to 
>descriptors.
>

DCMD descriptor attributes remain same for any host and also task parameters as QBR need to be enabled with DCMD.
So I believe it should be ok if we just add callback to allow hosts to update command parameters of DCMD descriptor only thru cqhci_host_ops.

Also, don’t see any requirement for host specific Task parameter updates in Task descriptor so not sure if there is any need to provide callback for task descriptor data preparation to hosts.
Please confirm.

>>
>> What do people think?
>>
>>>   		} else {
>>>   			resp_type = 0x2;
>>>   			timing = 0x1;
>>> diff --git a/drivers/mmc/host/cqhci.h b/drivers/mmc/host/cqhci.h
>>> index 9e68286a07b4..f96d8565cc07 100644
>>> --- a/drivers/mmc/host/cqhci.h
>>> +++ b/drivers/mmc/host/cqhci.h
>>> @@ -170,6 +170,7 @@ struct cqhci_host {
>>>   
>>>   	u32 quirks;
>>>   #define CQHCI_QUIRK_SHORT_TXFR_DESC_SZ	0x1
>>> +#define CQHCI_QUIRK_CMD_TIMING_R1B_DCMD	0x2
>>>   
>>>   	bool enabled;
>>>   	bool halted;
>>>