On Tue, 2014-03-18 at 21:49 -0500, Hou Zhiqiang-B48286 wrote: > > > -----Original Message----- > > From: Wood Scott-B07421 > > Sent: Wednesday, March 19, 2014 6:09 AM > > To: Hou Zhiqiang-B48286 > > Cc: 'Geert Uytterhoeven'; Mark Brown; linux-spi@xxxxxxxxxxxxxxx; > > devicetree@xxxxxxxxxxxxxxx; rob.herring@xxxxxxxxxxx; pawel.moll@xxxxxxx; > > mark.rutland@xxxxxxx; ijc+devicetree@xxxxxxxxxxxxxx; galak@xxxxxxxxxxxxxx; > > grant.likely@xxxxxxxxxxxx; Hu Mingkai-B21284 > > Subject: Re: [PATCH 2/2] spi/fsl-lib: Get the SPI controller bus number > > from DTS > > > > On Tue, 2014-03-18 at 04:34 -0500, Hou Zhiqiang-B48286 wrote: > > > > > > > -----Original Message----- > > > > From: geert.uytterhoeven@xxxxxxxxx > > > > [mailto:geert.uytterhoeven@xxxxxxxxx] > > > > On Behalf Of Geert Uytterhoeven > > > > Sent: Tuesday, March 18, 2014 4:56 PM > > > > To: Hou Zhiqiang-B48286 > > > > Cc: Mark Brown; linux-spi@xxxxxxxxxxxxxxx; > > > > devicetree@xxxxxxxxxxxxxxx; rob.herring@xxxxxxxxxxx; > > > > pawel.moll@xxxxxxx; mark.rutland@xxxxxxx; > > > > ijc+devicetree@xxxxxxxxxxxxxx; galak@xxxxxxxxxxxxxx; > > > > grant.likely@xxxxxxxxxxxx; Wood Scott-B07421; Hu Mingkai-B21284 > > > > Subject: Re: [PATCH 2/2] spi/fsl-lib: Get the SPI controller bus > > > > number from DTS > > > > > > > > On Tue, Mar 18, 2014 at 8:40 AM, B48286@xxxxxxxxxxxxx > > > > <B48286@xxxxxxxxxxxxx> wrote: > > > > >> > > The DT already has support for specifying flash layouts, > > > > >> > > can't those be used (for example via chosen if they're not > > > > >> > > fixed for the > > > > board)? > > > > >> > > Or if it's just picking the correct filesystem then UUIDs and > > > > >> > > labels are the standard way to do things. > > > > >> > > > > >> > The DT specifying flash layouts is ok. There is another way to > > > > >> > make the flash layouts using command line, but it is not safe > > > > >> > because of the dynamic bus_num. It is not the reason that the > > > > >> > way of DT is supported flash layouts, to live the other way > > unsafe, right? > > > > >> > > > > >> This sounds to me like we need a better way of talking about > > > > >> flash device names on the Linux command line rather than a way to > > > > >> fix the bus number - for example, being able to refer to them > > > > >> using a fixed property like the physical address. Being able to > > > > >> refer to devices via an alias assigned in the DT would also be > > > > >> useful (and more readable), I think there may already be a > > > > >> mechanism for doing that which would need to be plumbed in but I'm > > not 100% sure. > > > > > > > > > > The bus number is the variable designed to distinguish one spi > > > > > controller from others. Why spi controller's physical address must > > > > > be use instead of bus number? > > > > > > > > Because the bus number is dynamic, while the physical address > > > > doesn't change, so it can be used to uniqely identify the device > > > > before booting the kernel. > > > > Cfr. "spi1" vs. "e6e20000.spi". > > > > > > > > > > The precondition of dynamic bus number is initial it with -1 in the > > > controller driver. But now I need a reasonable bus number, I don't want > > a dynamic one. > > > Why does use the controller's physical address to take the role of bus > > > number to distinguish controllers. > > > > Where are you going to get this "reasonable" non-dynamic number from? > > How are you going to ensure there are no conflicts with other SPI > > controllers (e.g. on a dynamic add-on card)? > > > "other than negative (== assign one dynamically), bus_num is fully > board-specific. usually that simplifies to being SOC-specific. > example: one SOC has three SPI controllers, numbered 0..2, > and one board's schematics might show it using SPI-2. software > would normally use bus_num=2 for that controller." > The above paragraph is description of bus_num in spi.h. The "reasonable" > is from it. > Other controllers should also include this property, otherwise it will be > dynamic. So there is not conflict. So instead of using something concrete like a physical address, you want to use a number from a manual. Again, what happens in a system where SPI controllers can be added dynamically (forget about whether this is possible on the systems you care about), or even statically from a different source (e.g. board logic)? How does the driver know what number the manual assigns to a given controller? Why would you even want to deal with this when using the physical address is so easy? > > Physical addresses work well because they are tied to something real, > > rather than an arbitrary enumeration. Our NAND controllers use the > > physical address for the MTD name. Device tree NOR flash allows the > > device tree to set the mtd name[1], and otherwise falls back on the > > platform device name, which contains the physical address. > > > I know the physical work well, but there is a mechanism of bus number. > As the description say above, isn't it reasonable? No. -Scott -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
