linux-kernel - RE: [PATCH v2 8/9] PCI: rockchip: Use u32 variable to access 32-bit registers

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Date:   Wed, 15 Feb 2023 10:46:16 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Damien Le Moal' <damien.lemoal@...nsource.wdc.com>,
        Rick Wertenbroek <rick.wertenbroek@...il.com>,
        "alberto.dassatti@...g-vd.ch" <alberto.dassatti@...g-vd.ch>
CC:     "xxm@...k-chips.com" <xxm@...k-chips.com>,
        "rick.wertenbroek@...g-vd.ch" <rick.wertenbroek@...g-vd.ch>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        "Krzysztof Kozlowski" <krzysztof.kozlowski+dt@...aro.org>,
        Heiko Stuebner <heiko@...ech.de>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jani Nikula <jani.nikula@...el.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Mikko Kovanen <mikko.kovanen@...amobile.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-rockchip@...ts.infradead.org" 
        <linux-rockchip@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: RE: [PATCH v2 8/9] PCI: rockchip: Use u32 variable to access 32-bit
 registers

From: Damien Le Moal
> Sent: 15 February 2023 01:34
> 
> On 2/14/23 23:08, Rick Wertenbroek wrote:
> > Previously u16 variables were used to access 32-bit registers, this
> > resulted in not all of the data being read from the registers. Also
> > the left shift of more than 16-bits would result in moving data out
> > of the variable. Use u32 variables to access 32-bit registers
> >
> > Fixes: cf590b078391 ("PCI: rockchip: Add EP driver for Rockchip PCIe controller")
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Rick Wertenbroek <rick.wertenbroek@...il.com>
> > ---
> >  drivers/pci/controller/pcie-rockchip-ep.c | 10 +++++-----
> >  drivers/pci/controller/pcie-rockchip.h    |  1 +
> >  2 files changed, 6 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/pci/controller/pcie-rockchip-ep.c b/drivers/pci/controller/pcie-rockchip-ep.c
> > index ca5b363ba..b7865a94e 100644
> > --- a/drivers/pci/controller/pcie-rockchip-ep.c
> > +++ b/drivers/pci/controller/pcie-rockchip-ep.c
> > @@ -292,15 +292,15 @@ static int rockchip_pcie_ep_set_msi(struct pci_epc *epc, u8 fn, u8 vfn,
> >  {
> >  	struct rockchip_pcie_ep *ep = epc_get_drvdata(epc);
> >  	struct rockchip_pcie *rockchip = &ep->rockchip;
> > -	u16 flags;
> > +	u32 flags;
> >
> >  	flags = rockchip_pcie_read(rockchip,
> >  				   ROCKCHIP_PCIE_EP_FUNC_BASE(fn) +
> >  				   ROCKCHIP_PCIE_EP_MSI_CTRL_REG);
> >  	flags &= ~ROCKCHIP_PCIE_EP_MSI_CTRL_MMC_MASK;
> >  	flags |=
> > -	   ((multi_msg_cap << 1) <<  ROCKCHIP_PCIE_EP_MSI_CTRL_MMC_OFFSET) |
> > -	   PCI_MSI_FLAGS_64BIT;
> > +	   (multi_msg_cap << ROCKCHIP_PCIE_EP_MSI_CTRL_MMC_OFFSET) |
> 
> ROCKCHIP_PCIE_EP_MSI_CTRL_MMC_OFFSET is 17 and multi_msg_cap is a u8...
> Not nice.

It really doesn't matter.
As soon as you do any arithmetic char and short are promoted to int.

	David

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