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

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Date:   Fri, 8 Mar 2019 14:29:32 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Sowjanya Komatineni <skomatineni@...dia.com>,
        Ritesh Harjani <riteshh@...eaurora.org>,
        "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 7/03/19 8:16 PM, Sowjanya Komatineni wrote:
> 
>> 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.

That sounds fine to me.  Maybe do that for the next version of this patchset.

> 
> 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;
>>>>