linux-kernel - Re: ARC dw-mshc binding compat string

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Date:	Sat, 26 Mar 2016 19:10:11 +0100
From:	Marek Vasut <marex@...x.de>
To:	Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
CC:	linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
	Alexey Brodkin <abrodkin@...opsys.com>
Subject: Re: ARC dw-mshc binding compat string

On 03/26/2016 06:52 PM, Vladimir Zapolskiy wrote:
> Hi Marek,
> 
> On 26.03.2016 19:30, Marek Vasut wrote:
>> On 03/26/2016 06:26 PM, Vladimir Zapolskiy wrote:
>>> On 26.03.2016 12:14, Marek Vasut wrote:
>>>> Hi!
>>>>
>>>> I noticed that arch/arc/boot/dts/axs10x_mb.dtsi uses "altr," prefix in
>>>> the DT compatible string:
>>>>
>>>> mmc@...5000 {
>>>>         compatible = "altr,socfpga-dw-mshc";
>>>>         reg = < 0x15000 0x400 >;
>>>>         num-slots = < 1 >;
>>>>         fifo-depth = < 16 >;
>>>>         card-detect-delay = < 200 >;
>>>>         clocks = <&apbclk>, <&mmcclk>;
>>>>         clock-names = "biu", "ciu";
>>>>         interrupts = < 7 >;
>>>>         bus-width = < 4 >;
>>>> };
>>>>
>>>> I don't think this is OK, since ARC is unrelated to Altera, which is
>>>> what the "altr," prefix stands for. I think the socfpga-dw-mshc shim
>>>> should be extended with another compatibility string, something like
>>>> "snps,arc-dw-mshc" and the axs10x_mb.dtsi should be adjusted
>>>> accordingly. What do you think ?
>>>>
>>>
>>> There is "snps,dw-mshc" described in
>>> Documentation/devicetree/bindings/mmc/synopsys-dw-mshc.txt and supported by
>>> dw_mmc host controller driver.
>>
>> Thanks, that's even better.
>>
>> btw what do you think of using altr, prefix on non-altera system, that
>> doesn't seem ok, right ?
> 
> according to ePAPR the prefix should represent a device (IP block here
> I believe) manufacturer, so it should be okay to use "altr" prefix on
> non-Altera system, if Altera provides  another hardware vendor with
> some own IP block.

In this case, it's Synopsys who provides the SD/MMC/MS core to other
chip makers (Altera etc).

> That said, I would rather prefer to see "snps,dw-mshc" prefix on description
> of an MMC controller found on SoCFPGA series, "altr,socfpga-dw-mshc" seems
> to be redundant.

According to drivers/mmc/host/dw_mmc-pltfm.c , the Altera SoCFPGA one
"altr,socfpga-dw-mshc" and also Imagination Technology Pistacio one
"img,pistachio-dw-mshc" need specialty bit (SDMMC_CMD_USE_HOLD_REG),
while the stock one "snps,dw-mshc" does not. I am not sure if the ARC
one needs it as well, but most likely yes.

I wonder if that bit is needed on some particular version of the DWMMC
core. In that case, should we have "snps,dw-mshc" and "snps,dw-mshc-vN"
binding ? Or should we use DT property to discern the need for this bit ?

> --
> With best wishes,
> Vladimir
> 


-- 
Best regards,
Marek Vasut