errr.. please ignore On Wed, 31 Mar 2004, Muthukumar Ratty wrote: > > embedded 101 > ------------ > use volatile variables. > Muthu. > > > On Thu, 1 Apr 2004, Mandeep Singh Sandhu wrote: > > > hi all, > > > > i'm facing a problem while reseting a chip. > > to reset the chip (RTL8139) i write a byte into it's > > command reg. and wait for the a bit to be 0 which > > indicates that the reset is complete. > > > > to test this bit i had first written a tight while loop > > as follows > > > > while((readb(ChipCmdReg) & ResetCmd) == 0); > > > > but the comp used to hang when it used reach this loop. > > it never came out. > > > > then i wrote: > > i = 1000; > > while(i) > > if((readb(ChipCmdReg) & ResetCmd) == 0) > > break; > > else > > i--; > > > > this worked! > > can ne one tell why the first way of testing the reset bit does not > > work, is it b'cos of some CPU caching, cos i also inserted a rmb() > > call but that too did not help. > > > > TIA > > > > - /dev/mandeep > > > > > > -----Original Message----- > > From: Curran, Dominic [mailto:dcurran@ti.com] > > Sent: Thursday, March 25, 2004 11:12 PM > > To: Mandeep Singh Sandhu; kernelnewbies@nl.linux.org > > Subject: RE: PCI DMA mapping question > > > > > > > > I was under the impression that GFP_DMA was only needed if you were > > allocating memory to be used with the ISA bus. At least on x86 the PCI bus > > can perform DMA on any 32-bit memory address. > > > > ISA (presumably because it's a 16-bit bus) can only access memory from 0 to > > 16MB, and this is why GFP_DMA is needed. > > > > Am I completely wrong ? > > > > dom > > > > > > > > -----Original Message----- > > From: Momchil Velikov [mailto:velco@fadata.bg] > > Sent: Thursday, March 25, 2004 3:19 PM > > To: Mandeep Singh Sandhu > > Subject: Re: PCI DMA mapping question > > > > > > >>>>> "Mandeep" == Mandeep Singh Sandhu <mandeep_sandhu@infosys.com> > > >>>>> writes: > > > > Mandeep> if i'm allocating by transmit and recieve buffers, > > Mandeep> for my ethernet driver, using pci_alloc_consistent then do i > > Mandeep> need to establish bounce buffers as well in case i get a > > Mandeep> mapping in a non-DMA zone?? but in Rubini's book it's written - > > Mandeep> "Allocation is handled in this function so that the buffer will > > Mandeep> be placed in a location that works with DMA..." > > > > That function checks the device addressing capabilities. It assumes that > > if a device can be addressed in a region with certain characteristics then > > *IT* can also address any region with the same characteristics. For > > example, if a device requested to be accessible for MMIO in a region under > > 1M, the kernel assumes that the device itself can address any region under > > 1M, thus it allocates page(s) with GFP_DMA set. > > > > Mandeep> so then do i need to keep bounce buffers?? > > > > I'm not sure what's the exact meaning of ``bounce buffer''. I tend to > > think that these ARE the bounce buffers (as opposed to having potentially > > larger buffers elsewhere or locking user pages for doing DMA to them). > > > > Mandeep> then it says that the allocation uses GFP_ATOMIC priority, > > Mandeep> shud'nt it use the GFP_DMA priority instead to ensure the > > Mandeep> addresses are allocated in the DMA zone?? > > > > GFP_ATOMIC and GPF_DMA are independent and can be set at once. GFP_ATOMIC > > means ``don't sleep'' (which, btw, is by no means ``atomic''), GPF_DMA means > > ``allocate under 1M''. > > > > ~velco > > > > -- > > Kernelnewbies: Help each other learn about the Linux kernel. > > Archive: http://mail.nl.linux.org/kernelnewbies/ > > FAQ: http://kernelnewbies.org/faq/ > > > > > > -- > > Kernelnewbies: Help each other learn about the Linux kernel. > > Archive: http://mail.nl.linux.org/kernelnewbies/ > > FAQ: http://kernelnewbies.org/faq/ > > > > > -- > Kernelnewbies: Help each other learn about the Linux kernel. > Archive: http://mail.nl.linux.org/kernelnewbies/ > FAQ: http://kernelnewbies.org/faq/ > -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
