On 20.04.2016 03:13, Oded Gabbay wrote: > On Tue, Apr 19, 2016 at 5:59 PM, Marek Olšák <mar...@gmail.com> wrote: >> On Tue, Apr 19, 2016 at 3:11 PM, Oded Gabbay <oded.gab...@gmail.com> wrote: >>> On Mon, Apr 18, 2016 at 6:03 PM, >>> Ilia Mirkin <imir...@alum.mit.edu> wrote: >>>> On Mon, Apr 18, 2016 at 10:47 AM, Oded Gabbay <oded.gab...@gmail.com> >>>> wrote: >>>>> On Thu, Apr 14, 2016 at 6:44 PM, Ilia Mirkin <imir...@alum.mit.edu> wrote: >>>>>> On Thu, Apr 14, 2016 at 11:08 AM, Oded Gabbay <oded.gab...@gmail.com> >>>>>> wrote: >>>>>>>> Wouldn't it make more sense to handle such issues in transfer_map? >>>>>>>> (i.e. create a staging memory area, and decode into it)? This assumes >>>>>>>> that the transfer_map() call has enough information to "do the right >>>>>>>> thing". I don't think it does today, but perhaps it could be taught? >>>>>>> It doesn't have all the info today, that's for sure. I imagine though >>>>>>> we can add parameters to it. >>>>>>> >>>>>>>> That way everything that's in a pipe_resource is in some >>>>>>>> tightly-controlled format, and we specify the LE <-> BE parameters >>>>>>>> when converting between CPU-read/written and GPU-read/written data. I >>>>>>>> believe this is a better match for what's really happening, too. What >>>>>>>> do you think? >>>>>>>> >>>>>>>> -ilia >>>>>>> >>>>>>> Unless I'm missing something, I think, at the end of the day, it will >>>>>>> be the same issues as in my solution - per code path per format is a >>>>>>> different case. That's because you will still need to "teach" >>>>>>> transfer_map, per each transfer per format what to do. So one will >>>>>>> need to go and debug every single code path there is in mesa for >>>>>>> drawing/copying/reading/textures/etc., like what I did in the last 1.5 >>>>>>> months. It's a great learning experience but it won't give anything >>>>>>> generic. >>>>>>> >>>>>>> Again, for example, in st_ReadPixels, I imagine you will need to give >>>>>>> "different orders" to transfer_map for the two different scenarios - >>>>>>> H/W blit and fallback. So what's the gain here ? >>>>>>> >>>>>>> If I'm missing something, please tell me. >>>>>> >>>>>> One of us is... let's figure out which one :) >>>>>> >>>>>> Here's my proposal: >>>>>> >>>>>> All data stored inside of resources is stored in a driver-happy >>>>>> format. The driver ensures that it's stored in proper endianness, etc. >>>>>> (Much like it does today wrt proper stride.) >>>>>> >>>>>> Blitting(/copying) between resources doesn't require any additional >>>>>> information, since you have the format(s) of the respective resources, >>>>>> and it's all inside the driver, so the driver does whatever it needs >>>>>> to do to make it all "work". >>>>>> >>>>>> *Accessing and modifying* resources (directly) from the CPU is what >>>>>> becomes tricky. The state tracker may have incorrect expectations of >>>>>> the actual backing data. There are a few different ways to resolve >>>>>> this. The one I'm proposing is that you only ever return a pointer to >>>>>> the directly underlying data if it matches the CPU's expectations >>>>>> (which will only be the case for byte-oriented array formats like >>>>>> PIPE_FORMAT_R8G8B8A8_* & co). Everything else, like e.g. >>>>>> PIPE_FORMAT_R5G6B5_UNORM and countless others, will have to go through >>>>>> a bounce buffer. >>>>>> >>>>>> At transfer map time, you convert the data from GPU-style to >>>>>> CPU-style, and copy back the relevant bits at unmap/flush time. >>>>>> >>>>>> This presents a nice clean boundary for this stuff. Instead of the >>>>>> state tracker trying to guess what the driver will do and feeding it >>>>>> endiannesses that it can't possibly guess properly, the tracking logic >>>>>> is relegated to the driver, and we extend the interfaces to allow the >>>>>> state tracker to access the data in a proper way. >>>>>> >>>>>> I believe the advantage of this scheme is that beyond adding format >>>>>> parameters to pipe_transfer_map() calls, there will not need to be any >>>>>> adjustments to the state trackers. >>>>>> >>>>>> One yet-to-be-resolved issue is what to do about glMapBuffer* - it >>>>>> maps a buffer, it's formatless (at map time), and yet the GPU will be >>>>>> required to interpret it correctly. We could decree that PIPE_BUFFER >>>>>> is just *always* an array of R8_UNORM and thus never needs any type of >>>>>> swapping. The driver needs to adjust accordingly to deal with accesses >>>>>> that don't fit that pattern (and where parameters can't be fed to the >>>>>> GPU to interpret it properly). >>>>>> >>>>>> I think something like the above will work. And I think it presents a >>>>>> cleaner barrier than your proposal, because none of the "this GPU can >>>>>> kinda-sorta understand BE, but not everywhere" details are ever >>>>>> exposed to the state tracker. >>>>>> >>>>>> Thoughts? >>>>>> >>>>>> -ilia >>>>> >>>>> Ilia, >>>>> >>>>> To make the GPU do a conversion during blitting, I need to configure >>>>> registers. This is done in a couple of functions in the r600g driver >>>>> (r600_translate_texformat, r600_colorformat_endian_swap, >>>>> r600_translate_colorformat and r600_translate_colorswap). >>>>> >>>>> The problem is that transfer_map/unmap don't call directly to those >>>>> functions. They call other functions which eventually call those 4 >>>>> functions. Among those "other" functions, there are several function >>>>> calls which are *not* in the r600g driver. i.e. we go back to generic >>>>> util functions. For example: >>>>> >>>>> #0 r600_translate_colorformat >>>>> #1 evergreen_init_color_surface >>>>> #2 evergreen_set_framebuffer_state >>>>> #3 util_blitter_custom_depth_stencil >>>>> #4 r600_blit_decompress_depth >>>>> #5 r600_texture_transfer_map >>>>> >>>>> Am I allowed to now pass information from transfer_map/unmap all the >>>>> way down to the 4 functions I mentioned through all these layers as >>>>> additional parameters ? I preferred to put it in pipe_resource as that >>>>> information goes all the way down to those functions, but if I can't >>>>> use that, then what's an acceptable alternative ? >>>>> >>>>> This time, I would like to get an agreement *before* I implement it. >>>> >>>> Probably a good idea. And as issues are investigated, people's >>>> opinions on the "correct" way might shift. Let's think about this... >>>> >>>> So clearly *a* correct way to handle this would be to stop all the >>>> lying. What's the lie? The lie is the PIPE_FORMAT. It talks about e.g. >>>> R5G6B5 but makes no mention of the byte layout in memory for those 16 >>>> bits. Really what we have right now is a format and an *implicit* >>>> endian ordering, which is the CPU's. But what happens when the CPU and >>>> GPU don't agree? >>>> >>>> There's a path we could take which would be to add an endianness >>>> alongside each format (be it by doubling formats, or an explicit >>>> second field). This would be a very far-reaching change though, and I >>>> doubt you'll want to do it. What we're left with is having a format >>>> and an *implicit* endianness. Which means that the consumers of the >>>> format need to be able to work out the implicit endianness involved. >>>> And the endianness will be GPU endian for regular resources, and CPU >>>> endian for "staging" resources. So it's definitely tempting to stick >>>> the endian thing into a private field of the resource, like Rob is >>>> suggesting - when creating a staging texture in >>>> transfer_map/unmap/flush, set the endianness the cpu endian. Otherwise >>>> set it to gpu endian. And I think this is somewhat similar to your >>>> former approach. >>>> >>>> What do you think? >>>> >>>> -ilia >>> >>> I don't think I have any other choice but to stick it as a private >>> field, because the endian parameter simple can't go through all the >>> function calls as an additional parameter. The reason is that >>> set_framebuffer_state() function types are called from >>> st_invalidate_state, where I don't have any idea about the "correct" >>> endianess, so I can't add the endian parameter to that function type. >>> >>> The only thing that is propagated through all layers is r600_texture. >>> I'll try to use that. >>> >>> Marek, Michel, >>> Do you think it is OK to add the endian mark to that private structure ? >> >> Yes, but doesn't util_format_description::is_array provide that info already? > > If you mean to say that they are interchangeable, than no. > It's true that for array formats we *never* need to do swaps, but for > non-array formats there are cases where we need to do it and cases > where we don't need to do it. > > For example, when writing to depth buffer through st_DrawPixels > (glDrawPixels) with GL_FLOAT, than the format used is > PIPE_FORMAT_Z32_FLOAT. > In the make_texture() part, we need to configure endian swap for the > staging buffer, but after you return from it and go into > st_create_texture_sampler_view(), you want the destination texture to > be configured without endian swapping.
So the CB/DB block can't swap bytes when accessing Z32? > Both those buffers are configured with PIPE_FORMAT_Z32_FLOAT, so > that's why is_array can't be used instead of a dedicated flag. Can't the driver figure out on its own whether it needs to swap or not based on other available information, e.g. considering the resource usage/bind flags and/or whether the resource is sampled from or rendered to? -- Earthling Michel Dänzer | http://www.amd.com Libre software enthusiast | Mesa and X developer _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev
