linux-kernel - Re: [PATCH v3 2/3] PCI: qcom-ep: Make use of PCIE_SPEED2MBS

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Message-ID: <20230928184808.GA12574@thinkpad>
Date:   Thu, 28 Sep 2023 20:48:08 +0200
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     lpieralisi@...nel.org, kw@...ux.com, andersson@...nel.org,
        konrad.dybcio@...aro.org, bhelgaas@...gle.com,
        linux-arm-msm@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, abel.vesa@...aro.org
Subject: Re: [PATCH v3 2/3] PCI: qcom-ep: Make use of PCIE_SPEED2MBS_ENC()
 macro for encoding link speed

On Wed, Sep 27, 2023 at 12:55:42PM -0500, Bjorn Helgaas wrote:
> On Wed, Sep 27, 2023 at 05:46:02PM +0200, Manivannan Sadhasivam wrote:
> > Instead of hardcoding the link speed in MBps, let's make use of the
> > existing PCIE_SPEED2MBS_ENC() macro that does the encoding of the
> > link speed for us. Also, let's Wrap it with QCOM_PCIE_LINK_SPEED_TO_BW()
> > macro to do the conversion to ICC speed.
> 
> In subject, /Make use of/Use/ would make better use of the subject
> line.  Lots of "uses" there :)
> 
> Above, s/let's//, and also s/make use of/use/.
> 

Ok, I will reword accordingly.

> > +#define QCOM_PCIE_LINK_SPEED_TO_BW(speed) \
> > +		Mbps_to_icc(PCIE_SPEED2MBS_ENC(pcie_link_speed[speed]))
> 
> It's a shame to have to duplicate this macro in pcie-qcom.c and in
> pcie-qcom-ep.c, especially since there's nothing qcom-specific in it.
> 
> Would a macro like this fit in interconnect.h?
> 

Unfortunately, no. This macro is neither interconnect specific nor PCI, but a
kind of both used by the driver. So it makes sense to keep it in the driver
itself for now.

If we happen to create a common header for host and ep drivers in the future, it
can be moved to that.

> > -	ret = icc_set_bw(pcie_ep->icc_mem, 0, MBps_to_icc(PCIE_GEN1_BW_MBPS));
> > +	ret = icc_set_bw(pcie_ep->icc_mem, 0, QCOM_PCIE_LINK_SPEED_TO_BW(1));
> 
> "1" is not very informative here.  Maybe PCIE_SPEED_2_5GT?  (I didn't
> completely verify that this is equivalent.)
> 

No. PCIE_SPEED_2_5GT is defined as 0x14 in pci.h. And I do not want to add a
macro for just "1" here.

- Mani

> Bjorn

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