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Date: Wed, 28 Feb 2024 12:17:09 +0530
From: Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
To: Bjorn Helgaas <helgaas@...nel.org>
CC: Bjorn Andersson <andersson@...nel.org>,
Konrad Dybcio
<konrad.dybcio@...aro.org>,
Lorenzo Pieralisi <lpieralisi@...nel.org>,
Krzysztof Wilczyński <kw@...ux.com>,
Rob Herring
<robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
Krzysztof Kozlowski
<krzysztof.kozlowski+dt@...aro.org>,
Conor Dooley <conor+dt@...nel.org>,
Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
Rob Herring
<robh+dt@...nel.org>,
Johan Hovold <johan+linaro@...nel.org>,
Brian Masney
<bmasney@...hat.com>, Georgi Djakov <djakov@...nel.org>,
<linux-arm-msm@...r.kernel.org>, <linux-pci@...r.kernel.org>,
<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<vireshk@...nel.org>, <quic_vbadigan@...cinc.com>,
<quic_skananth@...cinc.com>, <quic_nitegupt@...cinc.com>,
<quic_parass@...cinc.com>
Subject: Re: [PATCH v7 6/7] PCI: Bring out the pcie link speed to MBps logic
to new function
On 2/28/2024 5:55 AM, Bjorn Helgaas wrote:
> Mention the new interface name in the subject and in the commit log.
>
> s/pcie/PCIe/
>
> The subject says "to MBps", but the commit log says "to frequency".
>
> On Fri, Feb 23, 2024 at 08:18:03PM +0530, Krishna chaitanya chundru wrote:
>> Bring the switch case in pcie_link_speed_mbps to new function to
>> the header file so that it can be used in other places like
>> in controller driver.
>
> s/pcie_link_speed_mbps/pcie_link_speed_mbps()/ to identify it as a
> function.
>
>> Create a new macro to convert from MBps to frequency.
>
> Include the new macro name here.
>
> I think pcie_link_speed_mbps() returns Mb/s (mega*bits* per second),
> not MB/s (mega*bytes* per second).
>
>> Signed-off-by: Krishna chaitanya chundru <quic_krichai@...cinc.com>
>> ---
>> drivers/pci/pci.c | 19 +------------------
>> drivers/pci/pci.h | 24 ++++++++++++++++++++++++
>> 2 files changed, 25 insertions(+), 18 deletions(-)
>>
>> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
>> index d8f11a078924..b441ab862a8d 100644
>> --- a/drivers/pci/pci.c
>> +++ b/drivers/pci/pci.c
>> @@ -6309,24 +6309,7 @@ int pcie_link_speed_mbps(struct pci_dev *pdev)
>> if (err)
>> return err;
>>
>> - switch (to_pcie_link_speed(lnksta)) {
>> - case PCIE_SPEED_2_5GT:
>> - return 2500;
>> - case PCIE_SPEED_5_0GT:
>> - return 5000;
>> - case PCIE_SPEED_8_0GT:
>> - return 8000;
>> - case PCIE_SPEED_16_0GT:
>> - return 16000;
>> - case PCIE_SPEED_32_0GT:
>> - return 32000;
>> - case PCIE_SPEED_64_0GT:
>> - return 64000;
>> - default:
>> - break;
>> - }
>> -
>> - return -EINVAL;
>> + return pcie_link_speed_to_mbps(to_pcie_link_speed(lnksta));
>> }
>> EXPORT_SYMBOL(pcie_link_speed_mbps);
>>
>> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
>> index 2336a8d1edab..82e715ebe383 100644
>> --- a/drivers/pci/pci.h
>> +++ b/drivers/pci/pci.h
>> @@ -282,6 +282,30 @@ void pci_bus_put(struct pci_bus *bus);
>> (speed) == PCIE_SPEED_2_5GT ? 2500*8/10 : \
>> 0)
>>
>> +static inline int pcie_link_speed_to_mbps(enum pci_bus_speed speed)
>> +{
>> + switch (speed) {
>> + case PCIE_SPEED_2_5GT:
>> + return 2500;
>> + case PCIE_SPEED_5_0GT:
>> + return 5000;
>> + case PCIE_SPEED_8_0GT:
>> + return 8000;
>> + case PCIE_SPEED_16_0GT:
>> + return 16000;
>> + case PCIE_SPEED_32_0GT:
>> + return 32000;
>> + case PCIE_SPEED_64_0GT:
>> + return 64000;
>> + default:
>> + break;
>> + }
>> +
>> + return -EINVAL;
>> +}
>> +
>> +#define PCIE_MBS2FREQ(speed) (pcie_link_speed_to_mbps(speed) * 1000)
>
> I feel like I might have asked some of this before; if so, my
> apologies and maybe a comment would be useful here to save answering
> again.
>
> The MBS2FREQ name suggests that "speed" is Mb/s, but it's not; it's an
> enum pci_bus_speed just like PCIE_SPEED2MBS_ENC() takes.
>
> When PCI SIG defines a new data rate, PCIE_MBS2FREQ() will do
> something completely wrong when pcie_link_speed_to_mbps() returns
> -EINVAL. I think it would be better to do this in a way that we can
> warn about the unknown speed and fall back to some reasonable default
> instead of whatever (-EINVAL * 1000) works out to.
>
As commented below I will move PCIE_MBS2FREQ to qcom driver and I will
take care about -EINVAL in the qcom driver itself.
> PCIE_MBS2FREQ() looks an awful lot like PCIE_SPEED2MBS_ENC(), except
> that it doesn't adjust for the encoding overhead and it multiplies by
> 1000. I don't know what that result means. The name suggests a
> frequency?
>
> pcie_link_speed_to_mbps(PCIE_SPEED_2_5GT) == 2500 Mbit/s (raw data rate)
> PCIE_SPEED2MBS_ENC(PCIE_SPEED_2_5GT) == 2000 Mbit/s or 2 Gbit/s (effective data rate)
> PCIE_MBS2FREQ(PCIE_SPEED_2_5GT) == 2500000 (? 2.5M of something)
>
> I don't really know how OPP works, but it looks like maybe
> PCIE_MBS2FREQ() is a shim that depends on how the OPP tables in DT are
> encoded? I'm surprised that the DT OPP tables aren't encoded with
> either the raw data rate or the effective data rate directly instead
> of what looks like the raw data rate / 1000.
>
> Is this a standard OPP encoding that will apply to other drivers? If
> so, it would be helpful to point to where that encoding is defined.
> If not, PCIE_MBS2FREQ() should probably be defined in pcie-qcom.c.
>
It depends on how driver use OPP, I think as you suggested PCIE_MBS2FREQ
should belong to pcie-qcom.c as no other driver is using it for now.
I will move to pcie_qcom.c in my next series.
- Krishna Chaitanya.
> Bjorn
>
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