[PATCH v6 08/17] drm/msm/dsi/phy: Fix reading zero as PLL rates when unprepared

[Dmitry Baryshkov]

On 18/06/2025 16:54, Krzysztof Kozlowski wrote:
> On 18/06/2025 15:39, Dmitry Baryshkov wrote:
>> On 18/06/2025 16:34, Krzysztof Kozlowski wrote:
>>> On 18/06/2025 15:07, Dmitry Baryshkov wrote:
>>>> On Wed, Jun 18, 2025 at 10:28:10AM +0200, Krzysztof Kozlowski wrote:
>>>>> On 13/06/2025 16:04, Dmitry Baryshkov wrote:
>>>>>> On 13/06/2025 17:02, Krzysztof Kozlowski wrote:
>>>>>>> On 13/06/2025 15:55, Dmitry Baryshkov wrote:
>>>>>>>>>     
>>>>>>>>> @@ -361,24 +373,47 @@ static int dsi_pll_7nm_lock_status(struct dsi_pll_7nm *pll)
>>>>>>>>>     
>>>>>>>>>     static void dsi_pll_disable_pll_bias(struct dsi_pll_7nm *pll)
>>>>>>>>>     {
>>>>>>>>> +	unsigned long flags;
>>>>>>>>>     	u32 data;
>>>>>>>>>     
>>>>>>>>> +	spin_lock_irqsave(&pll->pll_enable_lock, flags);
>>>>>>>>> +	--pll->pll_enable_cnt;
>>>>>>>>> +	if (pll->pll_enable_cnt < 0) {
>>>>>>>>> +		spin_unlock_irqrestore(&pll->pll_enable_lock, flags);
>>>>>>>>> +		DRM_DEV_ERROR_RATELIMITED(&pll->phy->pdev->dev,
>>>>>>>>> +					  "bug: imbalance in disabling PLL bias\n");
>>>>>>>>> +		return;
>>>>>>>>> +	} else if (pll->pll_enable_cnt > 0) {
>>>>>>>>> +		spin_unlock_irqrestore(&pll->pll_enable_lock, flags);
>>>>>>>>> +		return;
>>>>>>>>> +	} /* else: == 0 */
>>>>>>>>> +
>>>>>>>>>     	data = readl(pll->phy->base + REG_DSI_7nm_PHY_CMN_CTRL_0);
>>>>>>>>>     	data &= ~DSI_7nm_PHY_CMN_CTRL_0_PLL_SHUTDOWNB;
>>>>>>>>>     	writel(0, pll->phy->pll_base + REG_DSI_7nm_PHY_PLL_SYSTEM_MUXES);
>>>>>>>>>     	writel(data, pll->phy->base + REG_DSI_7nm_PHY_CMN_CTRL_0);
>>>>>>>>> +	spin_unlock_irqrestore(&pll->pll_enable_lock, flags);
>>>>>>>>>     	ndelay(250);
>>>>>>>>
>>>>>>>> What is this ndelay protecting? Is is to let the hardware to wind down
>>>>>>>> correctly? I'm worried about dsi_pll_disable_pll_bias() beng followed up
>>>>>>>> by dsi_pll_enable_pll_bias() in another thread, which would mean that
>>>>>>>> corresponding writes to the REG_DSI_7nm_PHY_CMN_CTRL_0 can come up
>>>>>>>> without any delay between them.
>>>>>>>>
>>>>>>>
>>>>>>> Great question, but why do you ask me? The code was there already and
>>>>>>> MSM DRM drivers are not something I know and could provide context about.
>>>>>>
>>>>>> Because it's you who are changing the code as you've faced the issue
>>>>>> with recalc_rate.
>>>>>>
>>>>> Heh, the answer is then: I don't know. I think authors of the code could
>>>>> know.
>>>>
>>>> The 10nm HPG documents a 250ns interval between enabling PLL bias and
>>>> and enabling the PLL via the CMN_PLL_CNTRL register. There is no extra
>>>> delay between disabling the PLL, disabling FIFO and remobing PLL bias.
>>>> Please adjust the code for 7nm and 10nm PHYs accordingly.
>>>>
>>>>
>>>
>>> I can drop this 250 ns here, if that's what you ask me. But fixing
>>> anything in 10nm is not relevant to this patchset. You were already
>>> asking me for different fixes for some different things and I find it
>>> not acceptable anymore. Stop blocking this patchset with every little
>>> existing issue.
>>
>> I think that it is a common practice to ask to fix the issue in relevant
> 
> No, it is not.
> 
> It is common practice to fix things everywhere, but you rejecting the
> patches on that basis (coming again with some requests for unrelated
> issues) is not common and not correct.
> 
>> pieces. For example, we frequently ask to fix all the DT files if there
>> was an issue / workaround reported against a selected set of those.
> 
> And you reject the submitted fix of one DT file based because
> contributor did not fix the rest? Really? Since when do you employ such
> practice?

On a case-by-case basis. See the USB snps workarounds for an example.

> 
>>
>> In this case you can send a fix for 10nm separately, but please post a
>> fix for that platform too.
>>
>>>
>>> Or merge this code without this patch if a fix for reading PLL as zero
>>> anyhow is questionable for you.
>>
>> I think I've asked it at some point, to split the generic code parts and
>> the DSI enablement into two different patch series, so that they could
>> be picked up separately.
>>
>> No, the fix is not questionable. The patch causes questions though.
> 
> I have no interests in fixing DRM code. This is not my subsystem, this
> is not part I am responsible for. If it raises questions, why not
> devoting your time to fix it?

Then why are you submitting patches towards the DRM driver? I think the 
usual rules apply, you not having interest doesn't lower the bar for 
your submissions.

> 
> Best regards,
> Krzysztof


-- 
With best wishes
Dmitry