linux-kernel - Re: [PATCH v5 2/2] PCI: mediatek: Set up class type and vendor ID for MT7622

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Date:   Fri, 16 Mar 2018 12:15:03 +0000
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Honghui Zhang <honghui.zhang@...iatek.com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>, bhelgaas@...gle.com,
        matthias.bgg@...il.com, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        yingjoe.chen@...iatek.com, eddie.huang@...iatek.com,
        ryder.lee@...iatek.com, hongkun.cao@...iatek.com,
        youlin.pei@...iatek.com, yong.wu@...iatek.com,
        yt.shen@...iatek.com, sean.wang@...iatek.com,
        xinping.qian@...iatek.com
Subject: Re: [PATCH v5 2/2] PCI: mediatek: Set up class type and vendor ID
 for MT7622

On Wed, Jan 03, 2018 at 02:39:04PM +0800, Honghui Zhang wrote:
> On Tue, 2018-01-02 at 10:56 +0000, Lorenzo Pieralisi wrote:
> > On Thu, Dec 28, 2017 at 09:39:12AM +0800, Honghui Zhang wrote:
> > > On Wed, 2017-12-27 at 12:45 -0600, Bjorn Helgaas wrote:
> > > > On Wed, Dec 27, 2017 at 08:59:54AM +0800, honghui.zhang@...iatek.com wrote:
> > > > > From: Honghui Zhang <honghui.zhang@...iatek.com>
> > > > > 
> 
> > > > > +		/* Set up class code for MT7622 */
> > > > > +		val = PCI_CLASS_BRIDGE_PCI << 16;
> > > > > +		writel(val, port->base + PCIE_CONF_CLASS);
> > > > 
> > > > 1) Your comments mention MT7622 specifically, but this code is run for
> > > > both mt2712-pcie and mt7622-pcie.  If this code is safe and necessary
> > > > for both mt2712-pcie and mt7622-pcie, please remove the mention of
> > > > MT7622.
> > > 
> > > Hmm, the code snippet added here will only be executed by MT7622, since
> > > MT2712 will not enter this  "if (pcie->base) {"  condition.
> > > Should the mention of MT7622 must be removed in this case?
> > 
> > You should add an explicit way (eg of_device_is_compatible() match for
> > instance) to apply the quirk just on the platform that requires it.
> > 
> > Checking for "if (pcie->base)" is really not the way to do it.
> > 
> 
> hi, Lorenzo,
> Thanks very much for your advise.
> Passing the compatible string or platform data into this function needed
> to add some new field in the struct mtk_pcie_port, then I guess both set
> it for MT2712 and MT7622 is an easy way, since re-setting those values
> for MT2712 is safe.
> 
> > > > 2) The first comment mentions both "vendor ID and device ID" but you
> > > > don't write the device ID.  Since this code applies to both
> > > > mt2712-pcie and mt7622-pcie, my guess is that you don't *want* to
> > > > write the device ID.  If that's the case, please fix the comment.
> > > > 
> > > 
> > > My bad, I did not check the comments carefully.
> > > Thanks.
> > > 
> > > > 3) If you only need to set the vendor ID, you're performing a 32-bit
> > > > write (writel()) to update a 16-bit value.  Please use writew()
> > > > instead.
> > > > 
> > > 
> > > Ok, thanks, I guess I could use the following code snippet in the next
> > > version:
> > > val = readl(port->base + PCIE_CONF_VENDOR_ID)
> > > val &= ~GENMASK(15, 0);
> > > val |= PCI_VENDOR_ID_MEDIATEK;
> > > writel(val, port->base + PCIE_CONF_VENDOR_ID);
> > 
> > Have you read Bjorn's comment ? Or there is a problem with using
> > a writew() ?
> > 
> 
> This control register is a 32bit register, I'm not sure whether the apb
> bus support write an 16bit value with 16bit but not 32bit address
> alignment. I prefer the more safety old way of writel.
> 
> I need to do more test about the writew if the code elegant is more
> important.

I will mark this patch as "Changes Requested" waiting for a new
version, thanks.

Lorenzo