Re: [PATCH 2/3] mmc: dw_mmc: add dw_mmc-k3 for k3 platform

[zhangfei <zhangfei.gao@linaro.org>]

On 12/30/2013 10:32 AM, Zhangfei Gao wrote:
> On Mon, Dec 30, 2013 at 7:55 AM, Jaehoon Chung <jh80.chung@samsung.com> wrote:
>> On 12/30/2013 06:05 AM, Arnd Bergmann wrote:
>>> On Saturday 28 December 2013, Zhangfei Gao wrote:
>>>> Add dw_mmc-k3.c for k3v2, support sd/emmc
>>>>
>>>> Signed-off-by: Zhangfei Gao <zhangfei.gao@linaro.org>
>>>> Signed-off-by: Zhigang Wang <brooke.wangzhigang@huawei.com>
>>>> ---
>>>>   .../devicetree/bindings/mmc/k3-dw-mshc.txt         |   60 ++++++++++
>>>>   drivers/mmc/host/Kconfig                           |   10 ++
>>>>   drivers/mmc/host/Makefile                          |    1 +
>>>>   drivers/mmc/host/dw_mmc-k3.c                       |  126 ++++++++++++++++++++
>>>>   4 files changed, 197 insertions(+)
>>>>   create mode 100644 Documentation/devicetree/bindings/mmc/k3-dw-mshc.txt
>>>>   create mode 100644 drivers/mmc/host/dw_mmc-k3.c
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/mmc/k3-dw-mshc.txt b/Documentation/devicetree/bindings/mmc/k3-dw-mshc.txt
>>>> new file mode 100644
>>>> index 000000000000..d7e2d7f159bb
>>>> --- /dev/null
>>>> +++ b/Documentation/devicetree/bindings/mmc/k3-dw-mshc.txt
>>>> @@ -0,0 +1,60 @@
>>>> +* Hisilicon specific extensions to the Synopsys Designware Mobile
>>>> +  Storage Host Controller
>>>> +
>>>> +Read synopsys-dw-mshc.txt for more details
>>>> +
>>>> +The Synopsys designware mobile storage host controller is used to interface
>>>> +a SoC with storage medium such as eMMC or SD/MMC cards. This file documents
>>>> +differences between the core Synopsys dw mshc controller properties described
>>>> +by synopsys-dw-mshc.txt and the properties used by the Hisilicon specific
>>>> +extensions to the Synopsys Designware Mobile Storage Host Controller.
>>>> +
>>>> +Required Properties:
>>>> +
>>>> +* compatible: should be one of the following.
>>>> +  - "hisilicon,hi4511-dw-mshc": for controllers with hi4511 specific extentions.
>>>
>>> I wonder if this is actually a different variant of the mshc hardware, or just
>>> wired up in a different way. Do you know details?
>>>
>>> Since the only difference in the binding is the presence of the "clock-freq-table"
>>> property, we could also make this property generic for the mshc driver and use
>>> it if present but fall back to the normal behavior when it is absent.
>
> There are still other differences and limitations besides "clock-freq-table".
> The controller seems less intelligent than other Synopsys mmc controller.
> The tuning process like HS200 is not intelligent, as a result, some
> local registers are added to help this.
>
>>>
>>>> +* clock-freq-table: should be the frequency (in Hz) array of the ciu clock
>>>> +    in each supported mode.
>>>> +    0. CIU clock rate in Hz for DS mode
>>>> +    1. CIU clock rate in Hz for MMC HS mode
>>>> +    2. CIU clock rate in Hz for SD HS mode
>>>> +    3. CIU clock rate in Hz for SDR12 mode
>>>> +    4. CIU clock rate in Hz for SDR25 mode
>>>> +    5. CIU clock rate in Hz for SDR50 mode
>>>> +    6. CIU clock rate in Hz for SDR104 mode
>>>> +    7. CIU clock rate in Hz for DDR50 mode
>>>> +    8. CIU clock rate in Hz for HS200 mode
>>>
>>> This looks god now.
>>>
>>>> +static void dw_mci_k3_set_ios(struct dw_mci *host, struct mmc_ios *ios)
>>>> +{
>>>> +    struct dw_mci_k3_priv_data *priv = host->priv;
>>>> +    u32 rate = priv->clk_table[ios->timing];
>>>> +    int ret;
>>>
>>> I think this should have some range checking to see if the mode that is
>>> being set had a clock frequency set in the DT.
>
> The range safety should be ensured by the clk_table array, MAX_NUMS=10.
>>>
>>>> +
>>>> +    ret = clk_set_rate(host->ciu_clk, rate);
>>>> +    if (ret)
>>>> +            dev_warn(host->dev, "failed to set clock rate %uHz\n", rate);
>>>> +
>>>> +    host->bus_hz = clk_get_rate(host->ciu_clk);
>>>> +}
>>>
>>> Why do you call clk_get_rate() here, shouldn't it always be the same
>>> rate that you have just set?
>
> It is more accurate to use clk_get_rate here.
> For example, if switch to ios->clock as you suggested before, 52M will
> be set for mmc, while 50M is supported.
> However, it can simply use rate set currently.
>
>>>
>>>> +static int dw_mci_k3_parse_dt(struct dw_mci *host)
>>>> +{
>>>> +    struct dw_mci_k3_priv_data *priv;
>>>> +    struct device_node *node = host->dev->of_node;
>>>> +    struct property *prop;
>>>> +    const __be32 *cur;
>>>> +    u32 val, num = 0;
>>>> +
>>>> +    priv = devm_kzalloc(host->dev, sizeof(*priv), GFP_KERNEL);
>>>> +    if (!priv) {
>>>> +            dev_err(host->dev, "mem alloc failed for private data\n");
>>>> +            return -ENOMEM;
>>>> +    }
>>>> +    host->priv = priv;
>>>> +
>>>> +    of_property_for_each_u32(node, "clock-freq-table", prop, cur, val) {
>>>> +            if (num >= MAX_NUMS)
>>>> +                    break;
>>>> +            priv->clk_table[num++] = val;
>>>> +    }
>>>> +    return 0;
>>>> +}
>>>
>>> If we make this property part of the generic binding, this function could
>>> also get moved to the main dw_mci driver.
>
> This may be not general.
> The controller does not generate the clock itself, and set rate to the
> outside clock source, which may be different according to the working
> mode.
>
>>>
>>>> +static int dw_mci_k3_suspend(struct device *dev)
>>>> +{
>>>> +    struct dw_mci *host = dev_get_drvdata(dev);
>>>> +    int ret = 0;
>>>> +
>>>> +    ret = dw_mci_suspend(host);
>>>
>>> You should never initialize local variables when they are set later in the
>>> function (the ret = 0 part above). For more complex functions, this prevents
>>> gcc from warning you about accidentally uninitialized uses.

I am sorry I may fall into the dead end, but still quite not understand 
this rule.
I alwayes thought it would be a good habit to init local variables before.
Do you mean it should NOT init local variable as much as possible and 
only init on demand, like solving the gcc warning.
Why not init the them at start in case random value cause unpredicted error?

>
> Frankly speaking, I didn't know this rule at all.
> Often see the warning before like “Variable to be used not initialized”,
> so preferred to init the local variable as much as possible.
> Looks like it is wrong.
>
>>>
>>>> +    if (!ret)
>>>> +            clk_disable_unprepare(host->ciu_clk);
>>>> +
>>>> +    return ret;
>>>> +}
>>>
>>> The suspend/resume code also looks very generic. Can't we make these the
>>> default for dw-mci? If you do both, you won't even need a k3 specific driver.
>>> I think in general we should try hard to add code like this to the common
>>> driver when there is a chance that it can be shared with other platforms.
>>
>> Dw-mmc has the LOW_POWER mode feature at CLKENA register,
>> this feature is running like clock-gating.
>> So i have known it didn't control clock enable/disable in dw-mmc.c.
>
> It is added here since we have to set special register when resume
> back, which has been abstracted to ciu_clk prepare operation.
>
>>
>> Best Regards,
>> Jaehoon Chung
>>
>>>
>>>        Arnd
>>>
>>
>>
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