[RESEND PATCH v3 5/7] PCI: dwc: all: Modify dbi accessors to access data of 4/2/1 bytes

Kishon Vijay Abraham I kishon at ti.com
Fri Mar 10 04:04:24 PST 2017


On Thursday 09 March 2017 08:18 PM, Niklas Cassel wrote:
> On 03/09/2017 07:39 AM, Kishon Vijay Abraham I wrote:
>> Previously dbi accessors can be used to access data of size 4
>> bytes. But there might be situations (like accessing
>> MSI_MESSAGE_CONTROL in order to set/get the number of required
>> MSI interrupts in EP mode) where dbi accessors must
>> be used to access data of size 2. This is in preparation for
>> adding endpoint mode support to designware driver.
> Hello Kishon
> I don't really like the idea of adding an extra argument to every existing read/write.
> Will not a read/write of length != 32 be quite uncommon compared to
> a read/write of length == 32?
> How about adding some defines to pcie-designware.h:
> #define dw_pcie_writel_dbi(pci, base, reg, val) dw_pcie_write_dbi(pci, base, reg, 0x4, val)
> #define dw_pcie_readl_dbi(pci, base, reg) dw_pcie_read_dbi(pci, base, reg, 0x4)
> That way we don't have to change every existing read/write.
> Is there a reason why we can't just do:
> vial = dw_pcie_readl_dbi(pci, base, MSI_MESSAGE_CONTROL);

MSI_MESSAGE_CONTROL is 0x52 (MSI capability offset + 2). I'm not sure if we can
do a readl that crosses the alignment boundary in all platforms. The other
option is to readl from "MSI capability offset + 0" and extract the last 16
bits. I felt this is more clear since we are interested only in the

> <shifting+masking the bits we need to get/set>
> dw_pcie_writel_dbi(pci, base, MSI_MESSAGE_CONTROL, val);
> Or are we going to be doing read/writes of length != 32 so often that
> you think that it's cleaner to have this abstraction?

it's used mainly for accessing configuration space header fields. Even the pci
core uses *pci_read_config_word* for accessing such fields.


More information about the linux-arm-kernel mailing list