[1/2] usb: host: tegra: don't touch EMC clock

From: Stephen Warren <swarren@nvidia.com>

Clock "emc" is for the External Memory Controller. The USB driver has no
business touching this clock directly. Remove the code that does so.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
---
Greg, Alan, I'd like to take this patch through the Tegra tree to avoid
any merge conflicts with the Tegra USB changes that have  recently
happened there.

Venu, When creating your patch to convert the Tegra USB PHY driver to a
platform driver, can you assume these patches are applied first? Thanks.
I assume that these patches make sense to you; could you ack them if so.
---
 drivers/usb/host/ehci-tegra.c |   17 -----------------
 1 file changed, 17 deletions(-)

On Tue, Jan 22, 2013 at 05:28:22PM -0700, Stephen Warren wrote:
> From: Stephen Warren <swarren@nvidia.com>
> 
> Clock "emc" is for the External Memory Controller. The USB driver has no
> business touching this clock directly. Remove the code that does so.
> 
> Signed-off-by: Stephen Warren <swarren@nvidia.com>
> ---
> Greg, Alan, I'd like to take this patch through the Tegra tree to avoid
> any merge conflicts with the Tegra USB changes that have  recently
> happened there.
> 
> Venu, When creating your patch to convert the Tegra USB PHY driver to a
> platform driver, can you assume these patches are applied first? Thanks.
> I assume that these patches make sense to you; could you ack them if so.
> ---
>  drivers/usb/host/ehci-tegra.c |   17 -----------------
>  1 file changed, 17 deletions(-)

I always love to see code deleted, so feel free to take this through
your tree:
	Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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> -----Original Message-----
> From: linux-tegra-owner@vger.kernel.org [mailto:linux-tegra-
> owner@vger.kernel.org] On Behalf Of Stephen Warren
> Sent: Wednesday, January 23, 2013 5:58 AM
> To: Alan Stern; Greg Kroah-Hartman; Stephen Warren
> Cc: Venu Byravarasu; linux-tegra@vger.kernel.org; linux-arm-
> kernel@lists.infradead.org; linux-usb@vger.kernel.org; Stephen Warren
> Subject: [PATCH 1/2] usb: host: tegra: don't touch EMC clock
> 
> From: Stephen Warren <swarren@nvidia.com>
> 
> Clock "emc" is for the External Memory Controller. The USB driver has no
> business touching this clock directly. Remove the code that does so.

Stephen,
This was primarily done to make sure that EMC is set to a minimum
frequency, below which data errors may occur during USB transfers.
If we plan to remove this, how should we make sure that the EMC
is programmed for the required frequency during USB transfers?
 
> 
> Signed-off-by: Stephen Warren <swarren@nvidia.com>
> ---
> Greg, Alan, I'd like to take this patch through the Tegra tree to avoid
> any merge conflicts with the Tegra USB changes that have  recently
> happened there.
> 
> Venu, When creating your patch to convert the Tegra USB PHY driver to a
> platform driver, can you assume these patches are applied first? Thanks.
> I assume that these patches make sense to you; could you ack them if so.
> ---
>  drivers/usb/host/ehci-tegra.c |   17 -----------------
>  1 file changed, 17 deletions(-)
> 
> diff --git a/drivers/usb/host/ehci-tegra.c b/drivers/usb/host/ehci-tegra.c
> index 1f596fb..b02622a 100644
> --- a/drivers/usb/host/ehci-tegra.c
> +++ b/drivers/usb/host/ehci-tegra.c
> @@ -44,7 +44,6 @@ struct tegra_ehci_hcd {
>  	struct ehci_hcd *ehci;
>  	struct tegra_usb_phy *phy;
>  	struct clk *clk;
> -	struct clk *emc_clk;
>  	struct usb_phy *transceiver;
>  	int host_resumed;
>  	int port_resuming;
> @@ -56,7 +55,6 @@ static void tegra_ehci_power_up(struct usb_hcd *hcd)
>  {
>  	struct tegra_ehci_hcd *tegra = dev_get_drvdata(hcd->self.controller);
> 
> -	clk_prepare_enable(tegra->emc_clk);
>  	clk_prepare_enable(tegra->clk);
>  	usb_phy_set_suspend(&tegra->phy->u_phy, 0);
>  	tegra->host_resumed = 1;
> @@ -69,7 +67,6 @@ static void tegra_ehci_power_down(struct usb_hcd
> *hcd)
>  	tegra->host_resumed = 0;
>  	usb_phy_set_suspend(&tegra->phy->u_phy, 1);
>  	clk_disable_unprepare(tegra->clk);
> -	clk_disable_unprepare(tegra->emc_clk);
>  }
> 
>  static int tegra_ehci_internal_port_reset(
> @@ -694,16 +691,6 @@ static int tegra_ehci_probe(struct platform_device
> *pdev)
>  	if (err)
>  		goto fail_clk;
> 
> -	tegra->emc_clk = devm_clk_get(&pdev->dev, "emc");
> -	if (IS_ERR(tegra->emc_clk)) {
> -		dev_err(&pdev->dev, "Can't get emc clock\n");
> -		err = PTR_ERR(tegra->emc_clk);
> -		goto fail_emc_clk;
> -	}
> -
> -	clk_prepare_enable(tegra->emc_clk);
> -	clk_set_rate(tegra->emc_clk, 400000000);
> -
>  	tegra->needs_double_reset = of_property_read_bool(pdev-
> >dev.of_node,
>  		"nvidia,needs-double-reset");
> 
> @@ -813,8 +800,6 @@ fail:
>  #endif
>  	usb_phy_shutdown(&tegra->phy->u_phy);
>  fail_io:
> -	clk_disable_unprepare(tegra->emc_clk);
> -fail_emc_clk:
>  	clk_disable_unprepare(tegra->clk);
>  fail_clk:
>  	usb_put_hcd(hcd);
> @@ -842,8 +827,6 @@ static int tegra_ehci_remove(struct platform_device
> *pdev)
> 
>  	clk_disable_unprepare(tegra->clk);
> 
> -	clk_disable_unprepare(tegra->emc_clk);
> -
>  	return 0;
>  }
> 
> --
> 1.7.10.4
> 
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Am Mittwoch, den 23.01.2013, 12:25 +0530 schrieb Venu Byravarasu:
> > -----Original Message-----
> > From: linux-tegra-owner@vger.kernel.org [mailto:linux-tegra-
> > owner@vger.kernel.org] On Behalf Of Stephen Warren
> > Sent: Wednesday, January 23, 2013 5:58 AM
> > To: Alan Stern; Greg Kroah-Hartman; Stephen Warren
> > Cc: Venu Byravarasu; linux-tegra@vger.kernel.org; linux-arm-
> > kernel@lists.infradead.org; linux-usb@vger.kernel.org; Stephen Warren
> > Subject: [PATCH 1/2] usb: host: tegra: don't touch EMC clock
> > 
> > From: Stephen Warren <swarren@nvidia.com>
> > 
> > Clock "emc" is for the External Memory Controller. The USB driver has no
> > business touching this clock directly. Remove the code that does so.
> 
> Stephen,
> This was primarily done to make sure that EMC is set to a minimum
> frequency, below which data errors may occur during USB transfers.
> If we plan to remove this, how should we make sure that the EMC
> is programmed for the required frequency during USB transfers?
>  
You could use something like the API I added in "ARM: tegra: add EMC
clock scaling API". This needs some rework and I looked into integrating
this with the DEVFREQ framework, but I don't think it fits too well.

Bandwidth requirements should always be communicated to the EMC driver
and not described by clock rates.

Regards,
Lucas

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On Tue, 22 Jan 2013, Stephen Warren wrote:

> From: Stephen Warren <swarren@nvidia.com>
> 
> Clock "emc" is for the External Memory Controller. The USB driver has no
> business touching this clock directly. Remove the code that does so.
> 
> Signed-off-by: Stephen Warren <swarren@nvidia.com>
> ---
> Greg, Alan, I'd like to take this patch through the Tegra tree to avoid
> any merge conflicts with the Tegra USB changes that have  recently
> happened there.

It's okay with me.

Acked-by: Alan Stern <stern@rowland.harvard.edu>

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On 01/23/2013 02:45 AM, Lucas Stach wrote:
> Am Mittwoch, den 23.01.2013, 12:25 +0530 schrieb Venu Byravarasu:
>>> -----Original Message-----
>>> From: linux-tegra-owner@vger.kernel.org [mailto:linux-tegra-
>>> owner@vger.kernel.org] On Behalf Of Stephen Warren
>>> Sent: Wednesday, January 23, 2013 5:58 AM
>>> To: Alan Stern; Greg Kroah-Hartman; Stephen Warren
>>> Cc: Venu Byravarasu; linux-tegra@vger.kernel.org; linux-arm-
>>> kernel@lists.infradead.org; linux-usb@vger.kernel.org; Stephen Warren
>>> Subject: [PATCH 1/2] usb: host: tegra: don't touch EMC clock
>>>
>>> From: Stephen Warren <swarren@nvidia.com>
>>>
>>> Clock "emc" is for the External Memory Controller. The USB driver has no
>>> business touching this clock directly. Remove the code that does so.
>>
>> Stephen,
>> This was primarily done to make sure that EMC is set to a minimum
>> frequency, below which data errors may occur during USB transfers.
>> If we plan to remove this, how should we make sure that the EMC
>> is programmed for the required frequency during USB transfers?
>
> You could use something like the API I added in "ARM: tegra: add EMC
> clock scaling API". This needs some rework and I looked into integrating
> this with the DEVFREQ framework, but I don't think it fits too well.
> 
> Bandwidth requirements should always be communicated to the EMC driver
> and not described by clock rates.

I agree.

Besides, on some boards there's an EMC scaling table defined already, so
the EMC driver is simply overriding the value the USB driver selects anyway.
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