linux-kernel - Re: [RFC PATCH] mmc: dw_mmc: remove redundant num

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Date:	Fri, 22 Jan 2016 14:04:03 +0900
From:	Jaehoon Chung <jh80.chung@...sung.com>
To:	Shawn Lin <shawn.lin@...k-chips.com>,
	Ulf Hansson <ulf.hansson@...aro.org>
Cc:	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] mmc: dw_mmc: remove redundant num_slots check

On 01/22/2016 12:07 PM, Shawn Lin wrote:
> On 2016/1/22 10:46, Jaehoon Chung wrote:
>> Hi, Shawn.
>>
>> On 01/21/2016 04:52 PM, Shawn Lin wrote:
>>> num_slots comes from pdata if existing, otherwise from
>>> dw_mci_parse_dt which make it at least one slot. If
>>> num_slots is less than 1 for the existing pdata case,
>>> current code return -ENODEV. But dw_mci_probe seems to
>>> treat this a optional case as it will call SDMMC_GET_SLOT_NUM
>>> if no slot assigned.
>>
>> Well, we need to consider more thing..
>> Host can get the number of slot from SDMMC_GET_SLOT_NUM().
>> But i think this way also has the problem.
>>
>> num_slot isn't defined anywhere, and num_slot should be set to value of SDMMC_GET_SLOT_NUM.
>> If that value is higher than 1, it should be blocking..(I didn't test all cases..)
>>
> 
> Actually, from the code itself, it confused me the way about how we get
> num_slot. At leaset, we might should try to cleanup it someway to make
> it a little more clear. And just as what you point out, we see some
> broblem here.
> 
>> Even though this patch is not correct, i could check the problem relevant to num_slot, because of this patch. :)
>>
> 
> Nice to here that. I make it a RFC patch since I also not quite sure
> about all cases including some corner cases. Let's think it twice.
> 
>> my suggestion is if pdata->num_slot is not defined anywhere, just set to 1 by default.
>> not take from SDMMC_GET_SLOT_NUM.
>>
> 
> yes, SDMMC_GET_SLOT_NUM is the capability of controller, num_slot is
> hardware wired number. So, geting it from SDMMC_GET_SLOT_NUM has
> problem.
> 
>> if (host->pdata->nums_slots < 1 ||
>>     host->pdata->nums_slots > SDMMC_GET_SLOT_NUM())
>>
>> This is correct condition. num_slots can't be higher than number of supported slots.
>> how about?
> 
> Seems reasonable.
> I guess you want to come up with a new patch dealing with it? :)

No matter who does this.
If you are ok, i will wait for patch. :)

Best Regards,
Jaehoon Chung

> 
>>
>> Best Regards,
>> Jaehoon Chung
>>
>>>
>>> Signed-off-by: Shawn Lin <shawn.lin@...k-chips.com>
>>>
>>> ---
>>>
>>>   drivers/mmc/host/dw_mmc.c | 6 ------
>>>   1 file changed, 6 deletions(-)
>>>
>>> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
>>> index 7128351..a116ec6 100644
>>> --- a/drivers/mmc/host/dw_mmc.c
>>> +++ b/drivers/mmc/host/dw_mmc.c
>>> @@ -2949,12 +2949,6 @@ int dw_mci_probe(struct dw_mci *host)
>>>           }
>>>       }
>>>
>>> -    if (host->pdata->num_slots < 1) {
>>> -        dev_err(host->dev,
>>> -            "Platform data must supply num_slots.\n");
>>> -        return -ENODEV;
>>> -    }
>>> -
>>>       host->biu_clk = devm_clk_get(host->dev, "biu");
>>>       if (IS_ERR(host->biu_clk)) {
>>>           dev_dbg(host->dev, "biu clock not available\n");
>>>
>>
>>
>>
>>
> 
>