| Message ID | e2c1bd6941e88f8988b1942c13c20cf436b3a963.1311936524.git.viresh.kumar@st.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, 2011-07-29 at 16:19 +0530, Viresh Kumar wrote: > Similar comment is present over routine also pl08x_choose_master_bus(). Keeping > one of them. Also rewrite that comment to convey message clearly. > > Signed-off-by: Viresh Kumar <viresh.kumar@st.com> > --- > drivers/dma/amba-pl08x.c | 11 +++-------- > 1 files changed, 3 insertions(+), 8 deletions(-) > > diff --git a/drivers/dma/amba-pl08x.c b/drivers/dma/amba-pl08x.c > index 1f7c510..4a64fdf 100644 > --- a/drivers/dma/amba-pl08x.c > +++ b/drivers/dma/amba-pl08x.c > @@ -498,9 +498,9 @@ struct pl08x_lli_build_data { > }; > > /* > - * Autoselect a master bus to use for the transfer this prefers the > - * destination bus if both available if fixed address on one bus the > - * other will be chosen > + * Autoselect a master bus to use for the transfer > + * - prefers the destination bus if both available > + * - if fixed address on one bus the other will be chosen Not sure I get it, English is not my first language :) > */ > static void pl08x_choose_master_bus(struct pl08x_lli_build_data *bd, > struct pl08x_bus_data **mbus, struct pl08x_bus_data **sbus, u32 cctl) > @@ -626,11 +626,6 @@ static int pl08x_fill_llis_for_desc(struct pl08x_driver_data *pl08x, > /* We need to count this down to zero */ > bd.remainder = txd->len; > > - /* > - * Choose bus to align to > - * - prefers destination bus if both available > - * - if fixed address on one bus chooses other > - */ > pl08x_choose_master_bus(&bd, &mbus, &sbus, cctl); > > dev_vdbg(&pl08x->adev->dev, "src=0x%08x%s/%u dst=0x%08x%s/%u len=%zu "
On 7/29/11, Koul, Vinod <vinod.koul@intel.com> wrote: > On Fri, 2011-07-29 at 16:19 +0530, Viresh Kumar wrote: >> /* >> - * Autoselect a master bus to use for the transfer this prefers the >> - * destination bus if both available if fixed address on one bus the >> - * other will be chosen >> + * Autoselect a master bus to use for the transfer >> + * - prefers the destination bus if both available >> + * - if fixed address on one bus the other will be chosen > Not sure I get it, English is not my first language :) Nor mine either. :) Will give some more explanation. But before that i wanted to know the exact purpose of this master-slave concept here. Probably it is for choosing the victim for reduction of width, in case src and dest addresses are misaligned to each other. @Russell and Linus: Is this correct? -- viresh
On Fri, Jul 29, 2011 at 08:47:06AM -0700, viresh kumar wrote: > On 7/29/11, Koul, Vinod <vinod.koul@intel.com> wrote: > > On Fri, 2011-07-29 at 16:19 +0530, Viresh Kumar wrote: > >> /* > >> - * Autoselect a master bus to use for the transfer this prefers the > >> - * destination bus if both available if fixed address on one bus the > >> - * other will be chosen > >> + * Autoselect a master bus to use for the transfer > >> + * - prefers the destination bus if both available > >> + * - if fixed address on one bus the other will be chosen > > Not sure I get it, English is not my first language :) > > Nor mine either. :) > > Will give some more explanation. > > But before that i wanted to know the exact purpose of this > master-slave concept here. > Probably it is for choosing the victim for reduction of width, in case > src and dest addresses > are misaligned to each other. > @Russell and Linus: Is this correct? No idea - most of the LLI code that's in this driver came from within ARM Ltd, and I've dared not change its behaviour in case the original author knew something that isn't public. In addition, as the ARM platforms I have with a PL080 on seem to have their DMA support buggered beyond belief (that's putting it mildly), I've not really been able to test anything more complex than single byte DMA to a UART. Linus W has one of the rare ARM platforms which has a working implementation. I'm not sure why the function is named in terms of master/slave because those terms don't seem to have much to do with what its actually doing (which is selecting either the source or destination to handle alignment issues with.) And it's not really about busses either. If the LLI creation code can be greatly simplified and that function killed off, that'd certainly be a great step forward. In the mean time I'd suggest leaving that comment as-is as long as the function exists.
2011/7/29 viresh kumar <viresh.linux@gmail.com>: > On 7/29/11, Koul, Vinod <vinod.koul@intel.com> wrote: >> On Fri, 2011-07-29 at 16:19 +0530, Viresh Kumar wrote: >>> /* >>> - * Autoselect a master bus to use for the transfer this prefers the >>> - * destination bus if both available if fixed address on one bus the >>> - * other will be chosen >>> + * Autoselect a master bus to use for the transfer >>> + * - prefers the destination bus if both available >>> + * - if fixed address on one bus the other will be chosen >> Not sure I get it, English is not my first language :) > > Nor mine either. :) > > Will give some more explanation. > > But before that i wanted to know the exact purpose of this > master-slave concept here. The PL08x has two bus mastering interfaces. They can be connected to two separate busses and two adress spaces even, usually that is not the case though. > Probably it is for choosing the victim for reduction of width, in case > src and dest addresses > are misaligned to each other. > @Russell and Linus: Is this correct? You can see from the function that it is only about choosing the master and slave. One of them is reading from some memory and one of them is writing. These are called source and destination respectively. What it then does is: - If one of the buses will be targeting a fixed address, choose the other one, so the one that increase address become master and the fixed address slave . - If both buses increas address (usually memory-to-memory) the third case is activated and deals with trying to set the widest bus as master. Crystal clear? Please copyedit/author something like the above... Thanks, Linus Walleij
On Sun, Jul 31, 2011 at 12:32:55AM +0200, Linus Walleij wrote: > 2011/7/29 viresh kumar <viresh.linux@gmail.com>: > > Nor mine either. :) > > > > Will give some more explanation. > > > > But before that i wanted to know the exact purpose of this > > master-slave concept here. > > The PL08x has two bus mastering interfaces. They can be > connected to two separate busses and two adress spaces > even, usually that is not the case though. This is not what the function is about... that's done by my pl08x_select_bus() function. This function (pl08x_choose_master_bus) does something completely different, and has to do with how the LLIs are laid out. I think it's to do with whether we use the source or destination for alignment purposes. It really has nothing to do with choosing busses.
2011/7/31 Russell King - ARM Linux <linux@arm.linux.org.uk>: > On Sun, Jul 31, 2011 at 12:32:55AM +0200, Linus Walleij wrote: >> The PL08x has two bus mastering interfaces. They can be >> connected to two separate busses and two adress spaces >> even, usually that is not the case though. > > This is not what the function is about... that's done by my > pl08x_select_bus() function. To be clear, I was explaining what I percieved as a question from Viresh about what the comment in this hunk of the patch was about: @@ -498,9 +498,9 @@ struct pl08x_lli_build_data { }; /* - * Autoselect a master bus to use for the transfer this prefers the - * destination bus if both available if fixed address on one bus the - * other will be chosen + * Autoselect a master bus to use for the transfer + * - prefers the destination bus if both available + * - if fixed address on one bus the other will be chosen */ static void pl08x_choose_master_bus(struct pl08x_lli_build_data *bd, struct pl08x_bus_data **mbus, struct pl08x_bus_data **sbus, u32 cctl) This is the comment just above pl08x_choose_master_bus(), the pl08x_lli_build_data() just has a danglig semicolon in the hunk. As for the LLI code, all of it's weird complexity comes from the fact that the DMAC cannot let a single element pass across 1KB (0x400) boundaries, which is one more than a little insane hardware restriction, and I have no clue where that limitation actually comes from, likely strange VHDL code. Then for this hunk: @@ -626,11 +626,6 @@ static int pl08x_fill_llis_for_desc(struct pl08x_driver_data *pl08x, /* We need to count this down to zero */ bd.remainder = txd->len; - /* - * Choose bus to align to - * - prefers destination bus if both available - * - if fixed address on one bus chooses other - */ pl08x_choose_master_bus(&bd, &mbus, &sbus, cctl); This is I think just redundant commenting of what the called function does, so yes should be deleted. Thanks, Linus Walleij
On 7/30/11, Linus Walleij <linus.walleij@linaro.org> wrote: > 2011/7/31 Russell King - ARM Linux <linux@arm.linux.org.uk>: >> On Sun, Jul 31, 2011 at 12:32:55AM +0200, Linus Walleij wrote: >>> The PL08x has two bus mastering interfaces. They can be >>> connected to two separate busses and two adress spaces >>> even, usually that is not the case though. >> >> This is not what the function is about... that's done by my >> pl08x_select_bus() function. > > To be clear, I was explaining what I percieved as a > question from Viresh about what the comment in this hunk of > the patch was about: > Just to clear my question again: - It wasn't about the comment but concept behind Master/Slave terminology. - Why are we referring src and dest as Master and Slave. As there is nothing like that. - As pointed by Russell and me earlier: Probably it is for choosing the victim for reduction of width, in case src and dest addresses are misaligned to each other. If what i understood is correct, then we should get rid of this routine or this master/slave terminology, as this is causing confusion. -- viresh
On Sun, Jul 31, 2011 at 01:37:46AM +0200, Linus Walleij wrote: > 2011/7/31 Russell King - ARM Linux <linux@arm.linux.org.uk>: > > On Sun, Jul 31, 2011 at 12:32:55AM +0200, Linus Walleij wrote: > >> The PL08x has two bus mastering interfaces. They can be > >> connected to two separate busses and two adress spaces > >> even, usually that is not the case though. > > > > This is not what the function is about... that's done by my > > pl08x_select_bus() function. > > To be clear, I was explaining what I percieved as a > question from Viresh about what the comment in this hunk of > the patch was about: Yes, and the comment and function name are wrong for what it's doing. I repeat: it has nothing to do with selecting an AHB bus. > As for the LLI code, all of it's weird complexity comes from the fact > that the DMAC cannot let a single element pass across 1KB (0x400) > boundaries, which is one more than a little insane hardware > restriction, and I have no clue where that limitation actually comes > from, likely strange VHDL code. Viresh's discussion with ARM Ltd indicates that this is not the case, and that restriction comes from misunderstanding of the documentation.
diff --git a/drivers/dma/amba-pl08x.c b/drivers/dma/amba-pl08x.c index 1f7c510..4a64fdf 100644 --- a/drivers/dma/amba-pl08x.c +++ b/drivers/dma/amba-pl08x.c @@ -498,9 +498,9 @@ struct pl08x_lli_build_data { }; /* - * Autoselect a master bus to use for the transfer this prefers the - * destination bus if both available if fixed address on one bus the - * other will be chosen + * Autoselect a master bus to use for the transfer + * - prefers the destination bus if both available + * - if fixed address on one bus the other will be chosen */ static void pl08x_choose_master_bus(struct pl08x_lli_build_data *bd, struct pl08x_bus_data **mbus, struct pl08x_bus_data **sbus, u32 cctl) @@ -626,11 +626,6 @@ static int pl08x_fill_llis_for_desc(struct pl08x_driver_data *pl08x, /* We need to count this down to zero */ bd.remainder = txd->len; - /* - * Choose bus to align to - * - prefers destination bus if both available - * - if fixed address on one bus chooses other - */ pl08x_choose_master_bus(&bd, &mbus, &sbus, cctl); dev_vdbg(&pl08x->adev->dev, "src=0x%08x%s/%u dst=0x%08x%s/%u len=%zu "
Similar comment is present over routine also pl08x_choose_master_bus(). Keeping one of them. Also rewrite that comment to convey message clearly. Signed-off-by: Viresh Kumar <viresh.kumar@st.com> --- drivers/dma/amba-pl08x.c | 11 +++-------- 1 files changed, 3 insertions(+), 8 deletions(-)