If the card has support for DMA i.e. it has a dma-controller on board, something like a PLX9080 then the card is 'bus-master capable' and you do want to exploit the DMA...I cannot think of a scenario where you would have a 'bus-master capable' board and choose not to use DMA.. HTH Learner --- Sumit Agarwal <aksumit@india.hp.com> wrote: > Most of the cards like SCSI, FC, NIC now include > their own > DMA engines. > Therefore it is good to have DMA for them. The older > cards > of EISA > that donot have their DMA engines needs to be set up > using > the DMA > controllers. Setting up of DMA controller is not a > over > head, as the > DMA is setup during the initialization. Later on > just the > channel is > selected and the locations are marked. This is > always going > to be > better than no DMA. The device driver writer is > aware of the > DMA > capabilities and generate the code. > > It is just the HBA (host bus adapter) or NIC that is > in > picture while > doing DMA and not the disk e.t.c that is present on > the > secondary > bus (like SCSI, IDE e.t.c). In PIO mode for every > byte/word > transaction > CPU intervention is required and hence is slow. > > Hope this helps, > Thanks, > Sumit > > Anand Tiwari wrote: > > > > i was going through the "understanding linux > kernel" and i was wondering that > > how the kernel or the device driver choose the > method for IO. > > is there any rule of thumb by which it decides > whether it should go for DMA > > or programmed IO. > > > > i m pretty confused .. please help me out ? > > anand > > > > ------------------------------------------------- > > This mail sent through IMP: http://horde.org/imp/ > > -- > > Kernelnewbies: Help each other learn about the > Linux kernel. > > Archive: > http://mail.nl.linux.org/kernelnewbies/ > > FAQ: http://kernelnewbies.org/faq/> begin:vcard > n:Agarwal;Sumit > tel;fax:(91)(80)2200196 > tel;home:+919845205210 > tel;work:2051126 > x-mozilla-html:FALSE > url:www.hp.com > org:HP-ISO;HPUX > version:2.1 > email;internet:aksumit@india.hp.com > title:Senior Software Engineer > adr;quoted-printable:;;Hewlett-Packard,=0D=0AIndia > Software Operation Pvt. Ltd.,=0D=0A29, Cunningham > Road,=0D=0A;Bangalore;Karnataka;560052;India > fn:Sumit Agarwal > end:vcard > __________________________________________________ Do you Yahoo!? HotJobs - Search new jobs daily now http://hotjobs.yahoo.com/ -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
