linux-kernel - Re: [RFC PATCH 1/7] mmc: sdhci: Add quirk to indicate no CRC stripping in MMC_RSP

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Date:   Thu, 17 Aug 2017 13:10:14 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Adrian Hunter <adrian.hunter@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Tony Lindgren <tony@...mide.com>,
        Rob Herring <robh+dt@...nel.org>
CC:     <nsekhar@...com>, <linux-omap@...r.kernel.org>,
        <linux-mmc@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 1/7] mmc: sdhci: Add quirk to indicate no CRC
 stripping in MMC_RSP_136



On Thursday 17 August 2017 12:01 PM, Adrian Hunter wrote:
> On 17/08/17 08:20, Kishon Vijay Abraham I wrote:
>> Hi Adrian,
>>
>> On Tuesday 15 August 2017 12:57 PM, Adrian Hunter wrote:
>>> On 07/08/17 19:01, Kishon Vijay Abraham I wrote:
>>>> TI's implementation of sdhci controller used in DRA7 SoC's doesn't
>>>> strip CRC in responses with length 136 bits. Add quirk to indicate
>>>> the controller does not strip CRC in MMC_RSP_136. If this quirk is
>>>> set sdhci library shouldn't shift the response present in
>>>> SDHCI_RESPONSE register.
>>>>
>>>> Signed-off-by: Kishon Vijay Abraham I <kishon@...com>
>>>> ---
>>>>  drivers/mmc/host/sdhci.c | 27 +++++++++++++++++++--------
>>>>  drivers/mmc/host/sdhci.h |  2 ++
>>>>  2 files changed, 21 insertions(+), 8 deletions(-)
>>>>
>>>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
>>>> index ecd0d4350e8a..ece3751d2a25 100644
>>>> --- a/drivers/mmc/host/sdhci.c
>>>> +++ b/drivers/mmc/host/sdhci.c
>>>> @@ -1182,14 +1182,25 @@ static void sdhci_finish_command(struct sdhci_host *host)
>>>>  
>>>>  	if (cmd->flags & MMC_RSP_PRESENT) {
>>>>  		if (cmd->flags & MMC_RSP_136) {
>>>> -			/* CRC is stripped so we need to do some shifting. */
>>>> -			for (i = 0;i < 4;i++) {
>>>> -				cmd->resp[i] = sdhci_readl(host,
>>>> -					SDHCI_RESPONSE + (3-i)*4) << 8;
>>>> -				if (i != 3)
>>>> -					cmd->resp[i] |=
>>>> -						sdhci_readb(host,
>>>> -						SDHCI_RESPONSE + (3-i)*4-1);
>>>> +			if (!(host->quirks2 & SDHCI_QUIRK2_NO_CRC_STRIPPING)) {
>>>
>>> This is about the 136-bit response so let's put that in the quirk name.  How about SDHCI_QUIRK2_RSP_136_HAS_CRC
>>
>> Since omap seems to be the only platform that doesn't have CRC, I prefer adding
>> SDHCI_QUIRK2_RSP_136_NO_CRC. That way we can add the quirk only in sdhci-omap
>> instead of all the existing sdhci drivers.
> 
> Except that it is the way I described.  All the others strip the CRC and we
> have to shift to pretend it is still there.

right. I made a totally bogus statement.

Thanks
Kishon