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/
