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 20:20:20 +0900
From:   Damien Le Moal <damien.lemoal@...nsource.wdc.com>
To:     David Laight <David.Laight@...LAB.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

On 2/15/23 19:46, David Laight wrote:
> 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.

OK. Thanks.


-- 
Damien Le Moal
Western Digital Research