Date:	Thu, 4 Sep 2014 10:58:41 +0200
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	Jean-Michel Hautbois <jean-michel.hautbois@...alys.com>
Cc:	Adrian Hunter <adrian.hunter@...el.com>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Shawn Guo <shawn.guo@...aro.org>,
	Dong Aisheng <b29396@...escale.com>,
	Peter Griffin <peter.griffin@...aro.org>,
	"tgih.jun@...sung.com" <tgih.jun@...sung.com>,
	h80.chung@...sung.com, Chris Ball <chris@...ntf.net>,
	Kumar Gala <galak@...eaurora.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Mark Rutland <mark.rutland@....com>,
	Pawel Moll <pawel.moll@....com>,
	Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH] mmc: sdhci-esdhc-imx: Enable boot partition access from DT

Hi

On 3 September 2014 15:08, Jean-Michel Hautbois
<jean-michel.hautbois@...alys.com> wrote:
> 2014-09-03 11:09 GMT+02:00 Ulf Hansson <ulf.hansson@...aro.org>:
>> On 3 September 2014 11:02, Adrian Hunter <adrian.hunter@...el.com> wrote:
>>> On 09/03/2014 11:30 AM, Ulf Hansson wrote:
>>>> On 2 September 2014 17:49, Jean-Michel Hautbois
>>>> <jean-michel.hautbois@...alys.com> wrote:
>>>>> This property is useful when we don't want to access boot partitions on eMMC
>>>>>
>>>>> Signed-off-by: Jean-Michel Hautbois <jean-michel.hautbois@...alys.com>
>>>>> ---
>>>>>  Documentation/devicetree/bindings/mmc/mmc.txt | 1 +
>>>>>  drivers/mmc/host/sdhci-esdhc-imx.c            | 8 ++++++++
>>>>>  include/linux/platform_data/mmc-esdhc-imx.h   | 1 +
>>>>>  3 files changed, 10 insertions(+)
>>>>>
>>>>> diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt b/Documentation/devicetree/bindings/mmc/mmc.txt
>>>>> index 431716e..59cc854 100644
>>>>> --- a/Documentation/devicetree/bindings/mmc/mmc.txt
>>>>> +++ b/Documentation/devicetree/bindings/mmc/mmc.txt
>>>>> @@ -40,6 +40,7 @@ Optional properties:
>>>>>  - mmc-hs200-1_2v: eMMC HS200 mode(1.2V I/O) is supported
>>>>>  - mmc-hs400-1_8v: eMMC HS400 mode(1.8V I/O) is supported
>>>>>  - mmc-hs400-1_2v: eMMC HS400 mode(1.2V I/O) is supported
>>>>> +- no-boot-part : when preset, tells to access boot partitions
>>>>>
>>>>>  *NOTE* on CD and WP polarity. To use common for all SD/MMC host controllers line
>>>>>  polarity properties, we have to fix the meaning of the "normal" and "inverted"
>>>>> diff --git a/drivers/mmc/host/sdhci-esdhc-imx.c b/drivers/mmc/host/sdhci-esdhc-imx.c
>>>>> index ccec0e3..439e663 100644
>>>>> --- a/drivers/mmc/host/sdhci-esdhc-imx.c
>>>>> +++ b/drivers/mmc/host/sdhci-esdhc-imx.c
>>>>> @@ -942,6 +942,11 @@ sdhci_esdhc_imx_probe_dt(struct platform_device *pdev,
>>>>>         if (of_property_read_u32(np, "fsl,delay-line", &boarddata->delay_line))
>>>>>                 boarddata->delay_line = 0;
>>>>>
>>>>> +       if (of_find_property(np, "no-boot-part", NULL))
>>>>> +               boarddata->access_boot_part = false;
>>>>> +       else
>>>>> +               boarddata->access_boot_part = true;
>>>>> +
>>>>>         return 0;
>>>>>  }
>>>>>  #else
>>>>> @@ -1119,6 +1124,9 @@ static int sdhci_esdhc_imx_probe(struct platform_device *pdev)
>>>>>                 host->quirks2 |= SDHCI_QUIRK2_NO_1_8_V;
>>>>>         }
>>>>>
>>>>> +       if (!boarddata->access_boot_part)
>>>>> +               host->mmc->caps2 |= MMC_CAP2_BOOTPART_NOACC;
>>>>> +
>>>>
>>>> Hmm, I don't think MMC_CAP2_BOOTPART_NOACC should have a DT binding.
>>>> Does it describe the hardware in some form?
>>>>
>>>> Actually I would like to question why MMC_CAP2_BOOTPART_NOACC exists
>>>> at all. If there are cards that don't supports the BOOT area,
>>>> shouldn't we have a card quirk for it instead of a host cap? Maybe
>>>> Adrian Hunter, how originally wrote the patch for adding
>>>> MMC_CAP2_BOOTPART_NOACC, could help me understand the reasons behind
>>>> it!?
>>>
>>> It was added because platform firmware was able to prevent access to the
>>> boot partitions (for security I think), so attempts to access them would
>>> fail messily.  It was not related to any specific card.
>>
>> Adrian, appreciate your clarification. After all it seems like adding
>> a DT binding for it should be appropriate.
>>
>> Kind regards
>> Uffe
>
> Thanks Adrian :).
> Well, there is boot partitions and rpmb partition, and maybe should we
> have a binding to prevent access to both of them ?
> Something else came to my mind, when you want to boot on eMMC, do you
> need to write u-boot in boot partitions or is it written at the
> logical adress 0 which is what fdisk uses as start ?
> Because, if this is not usuable but just scanned I can't see why we
> bother doing it... ?

Hi Jean-Michel,

I am not sure adding a DT binding for non access to rpmb would be
needed. At least until we heard of a similar case as Adrian describes
but for rpmb.

BTW, I just posted a patch which disabled partition scan of the boot
area, what to you think about that?
http://marc.info/?l=linux-mmc&m=140973496402028&w=2

Finally I am also wondering whether we could and thus should, handle
these situations entirely without using a host cap. In principle what
we need is a more sophisticated error handling when the switch errors
occurs, while trying to switch to the boot area/rpmb partitions. Could
you maybe investigate that option, before we decide to add a new DT
binding?

Kind regards
Uffe
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