Re: [PATCH] omapdss: use devm_clk_get()

[Archit Taneja <archit@ti.com>]

On Wednesday 10 April 2013 02:49 PM, Tomi Valkeinen wrote:
> On 2013-04-10 11:37, Archit Taneja wrote:
>> On Wednesday 10 April 2013 01:43 PM, Tomi Valkeinen wrote:
>>> On 2013-04-08 11:55, Archit Taneja wrote:
>>>> Use devm_clk_get() instead of clk_get() for dss, and for outputs hdmi
>>>> and venc.
>>>> This reduces reduces code and simplifies error handling.
>>>>
>>>> Signed-off-by: Archit Taneja <archit@ti.com>
>>>> ---
>>>>    drivers/video/omap2/dss/dss.c  |   18 +++---------------
>>>>    drivers/video/omap2/dss/hdmi.c |   16 ++--------------
>>>>    drivers/video/omap2/dss/venc.c |   10 +---------
>>>>    3 files changed, 6 insertions(+), 38 deletions(-)
>>>>
>>>> diff --git a/drivers/video/omap2/dss/dss.c
>>>> b/drivers/video/omap2/dss/dss.c
>>>> index 054c2a2..645b3bc 100644
>>>> --- a/drivers/video/omap2/dss/dss.c
>>>> +++ b/drivers/video/omap2/dss/dss.c
>>>> @@ -767,13 +767,11 @@ int dss_dpi_select_source(enum omap_channel
>>>> channel)
>>>>    static int dss_get_clocks(void)
>>>>    {
>>>>        struct clk *clk;
>>>> -    int r;
>>>>
>>>> -    clk = clk_get(&dss.pdev->dev, "fck");
>>>> +    clk = devm_clk_get(&dss.pdev->dev, "fck");
>>>>        if (IS_ERR(clk)) {
>>>>            DSSERR("can't get clock fck\n");
>>>> -        r = PTR_ERR(clk);
>>>> -        goto err;
>>>> +        return PTR_ERR(clk);
>>>>        }
>>>>
>>>>        dss.dss_clk = clk;
>>>> @@ -782,8 +780,7 @@ static int dss_get_clocks(void)
>>>>            clk = clk_get(NULL, dss.feat->clk_name);
>>>>            if (IS_ERR(clk)) {
>>>>                DSSERR("Failed to get %s\n", dss.feat->clk_name);
>>>> -            r = PTR_ERR(clk);
>>>> -            goto err;
>>>> +            return PTR_ERR(clk);
>>>>            }
>>>>        } else {
>>>>            clk = NULL;
>>>> @@ -792,21 +789,12 @@ static int dss_get_clocks(void)
>>>>        dss.dpll4_m4_ck = clk;
>>>>
>>>>        return 0;
>>>> -
>>>> -err:
>>>> -    if (dss.dss_clk)
>>>> -        clk_put(dss.dss_clk);
>>>> -    if (dss.dpll4_m4_ck)
>>>> -        clk_put(dss.dpll4_m4_ck);
>>>> -
>>>> -    return r;
>>>>    }
>>>
>>> Why didn't you use devm_clk_get for the dpll4_m4_ck clock also?
>>
>> clk_get of dpll4_m4_ck isn't tied to a device:
>>
>>      clk = clk_get(NULL, dss.feat->clk_name);
>>
>> We can't use devm_clk_get() if we don't tie it to a device, right?
>
> Ah, true.
>
>> I think the dss.dss_clk clock above is same as the dpll4_m4_ck for all
>> OMAPs. We could probably remove the dpll4_m4_clk all together, and use
>> dss_clk to get the rate of DSS_FCK coming from PRCM.
>
> Hmm, no, if I recall right, dpll4_m4_clk is the parent of dss clock (or
> parent of the parent of...), and the dss_fck_multiplier affects the
> resulting dss fck. Or something like that. It's a bit messy, especially
> as we can't just use the dss fck to change the rate, we need to change
> the rate at the parent for some reason.

Ah ok, I remember it now. One of the DPLL's divider's output is DSS_FCK. 
We get the parent's rate and iterate through all the possible hsdivider 
values to get the closest pixel clock. We don't/can't change 
dpll4_m4_clk as such, we just need to know it's rate for our calculations.

So yes, we need dpll4_m4_clk, we just need to rename it to a better 
thing. Like dss_clk_parent.

Anyway,
Archit