Re: [PATCH RFC 1/2] libahci_platform: add ahci_platform_get_of_property

From: Hans de Goede <hdegoede@redhat.com>
To: zhangfei <zhangfei.gao@linaro.org>, Mark Rutland <mark.rutland@arm.com>
Cc: "tj@kernel.org" <tj@kernel.org>, "arnd@arndb.de" <arnd@arndb.de>,
	"linux-ide@vger.kernel.org" <linux-ide@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>
Subject: Re: [PATCH RFC 1/2] libahci_platform: add ahci_platform_get_of_property
Date: Fri, 20 Jun 2014 09:38:31 +0200	[thread overview]
Message-ID: <53A3E4F7.4080504@redhat.com> (raw)
In-Reply-To: <53A3CD26.3070001@linaro.org>

Hi,

On 06/20/2014 07:56 AM, zhangfei wrote:
> 
> 
> On 06/19/2014 03:39 PM, Hans de Goede wrote:
>> Hi,
>>
>> On 06/19/2014 04:22 AM, zhangfei wrote:
>>> Hi Mark,
>>>
>>> On 06/18/2014 10:03 PM, Mark Rutland wrote:
>>>> On Wed, Jun 18, 2014 at 05:54:08AM +0100, Zhangfei Gao wrote:
>>>>> Instead of setting hflags in different files,
>>>>> ahci_platform_get_of_property set hpriv->flags when ahci_platform_init_host
>>>>> according to property in dts.
>>>>
>>>> The AHCI_HFLAGS are a Linux implementation detail, so it would be nice
>>>> to have a good justification for each of these being turned into DT
>>>> properties.
>>>
>>> Do you mean only add required property now?
>>
>> No you should not add any properties at all using properties to set SoC specific quirks
>> is just wrong, if a device is not 100% ahci compatible you should use a SoC specific
>> compatible string for it, and set quirks in the kernel driver based on that.
>>
>> Devicetree is supposed to describe hardware, in this case the quirks are a property
>> of the specific model of the hardware, so this should be expressed through the
>> compatible string. Extra properties in devicetree are meant to be used for board
>> specific things, like having a gpio to enable power to the sata target device.
>> Extra properties should not be used in the way you are proposing to use them now.
>>
> 
> OK, got it.
> 
> What I thoutht is using ahci_platform_get_of_property could make ahci_platform.c more shareable, adding the chance of removing specific compatible.
> Just refer mmc_of_parse and sdhci_get_of_property, they are parsing property directly from dts.

I'm not familiar with sdhci_get_of_property, but mmc_of_parse is all about
describing the board, not controller specific quirks. It sets things like
how many bits the sdcard slot has (just because the controller has x
bits does not mean they are all wired up), things like max speed (which again
is not only a host but also a board property), things like which gpio to use for
card detect, or if the mmc/sdio device is always present as it is soldered
onto the board, etc.

Regards,

Hans