Re: [PATCH] spi: qup: provide proper bus numbers

[Srinivas Kandagatla]

On 21/01/16 19:03, Mark Brown wrote:
> On Thu, Jan 21, 2016 at 06:47:34PM +0000, Srinivas Kandagatla wrote:
> > On 21/01/16 18:38, Mark Brown wrote:
> > > On Thu, Jan 21, 2016 at 06:33:47PM +0000, Srinivas Kandagatla wrote:
>
> > > > This driver reuses pdev->id for spi bus numbers resulting in random
> > > > or very large bus numbering when used with device trees. pdev->id
> > > > is not the correct choice when using device trees. So add code to
>
> > > What makes you say this, why is pdev->id not "correct"?  It is worrying
> > > if anything cares what number we pick.
>
> > Issue is that using pdev->id for bus number, as pdev->id does not get
> > populated in device tree cases.
>
> That's a statement of what currently happens...
>
> > The end users who are reading the schematics would not be able to map the
> > actual bus numbers on the schematics with the bus numbers allocated using
> > pdev->id. It add more confusion.
>
> > Without this patch the bus number allocated to this driver is 32766.
> > This does not really reflect the actual bus numbers on the boards
> > schematics.
>
> Is this really causing anyone any confusion?  Normally people are
> looking at the devices on the SPI bus rather than the bus itself...  In
> any case if this *is* causing confusion should we not be doing something
> at the bus core level that allows us to assign a descriptive name since
> this doesn't seem in the least bit SPI specific but could apply to any
> bus?
>
> There's also the problem that if someone has decided to label the bus
> with a descriptive name in their schematic (eg, "SPI_FLASH") then being
> able to assign a number doesn't do much to help, we'd need to be able to
> provide strings.  A brief survey of schematics I have to hand suggests
> that this is a thing people do.
>
> > > > get bus numbers via device tree aliases and if it fails then generate
> > > > a unique bus number.
>
> > > The other question is even if this is a good idea why is it something
> > > that should be open coded in individual drivers, if we want to change
> > > the policy we should be consistent between drivers.
>
> > Device tree aliases seems used very much in many drivers.
> > The unique bus number scheme was actually inspired by the
> > driver/tty/serial/msm_serial.c
>
> That doesn't help explain why it is a good idea to open code this in
> individual drivers.  I was asking why it's a good idea to do this in a
> single driver rather than at a higher level.

Oops!!, I should have looked at spi.c which already does exactly same 
thing. I think the logic did not get triggered because (int)-1 
overflowed into s16 busnum.

--srini

>