Messages in this thread | | | Subject | Re: [PATCH] mtd: nand: raw: atmel: add module param to avoid using dma | From | Peter Rosin <> | Date | Mon, 28 May 2018 17:52:53 +0200 |
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On 2018-05-28 16:27, Boris Brezillon wrote: > Hi Peter, > > On Mon, 28 May 2018 12:10:02 +0200 > Peter Rosin <peda@axentia.se> wrote: > >> On 2018-05-28 00:11, Peter Rosin wrote: >>> On 2018-05-27 11:18, Peter Rosin wrote: >>>> On 2018-05-25 16:51, Tudor Ambarus wrote: >>>>> We think the best way is to keep LCD on DDR Ports 2 and 3 (8th and 9th >>>>> slaves), to have maximum bandwidth and to use DMA on DDR port 1 for NAND >>>>> (7th slave). >>>> >>>> Exactly how do I accomplish that? >>>> >>>> I can see how I can move the LCD between slave DDR port 2 and 3 by >>>> selecting LCDC DMA master 8 or 9 (but according to the above it should >>>> not matter). The big question is how I control what slave the NAND flash >>>> is going to use? I find nothing in the datasheet, and the code is also >>>> non-transparent enough for me to figure it out by myself without >>>> throwing out this question first... >>> >>> I added this: >>> >>> diff --git a/drivers/mtd/nand/raw/atmel/nand-controller.c b/drivers/mtd/nand/raw/atmel/nand-controller.c >>> index e686fe73159e..3b33c63d2ed4 100644 >>> --- a/drivers/mtd/nand/raw/atmel/nand-controller.c >>> +++ b/drivers/mtd/nand/raw/atmel/nand-controller.c >>> @@ -1991,6 +1991,9 @@ static int atmel_nand_controller_init(struct atmel_nand_controller *nc, >>> nc->dmac = dma_request_channel(mask, NULL, NULL); >>> if (!nc->dmac) >>> dev_err(nc->dev, "Failed to request DMA channel\n"); >>> + >>> + dev_info(nc->dev, "using %s for DMA transfers\n", >>> + dma_chan_name(nc->dmac)); >>> } >>> >>> /* We do not retrieve the SMC syscon when parsing old DTs. */ >>> >>> >>> >>> and the output is >>> >>> atmel-nand-controller 10000000.ebi:nand-controller: using dma0chan5 for DMA transfers >>> >>> So, DMA controller 0 is in use. I still don't know if IF0, IF1 or IF2 is used >>> or how to find out. I guess IF2 is not in use since that does not allow any >>> DDR2 port as slave... >>> >>> From the datasheet, DMAC0/IF0 uses DDR2 Port 2, and DMAC0/IF1 uses DDR2 Port 1. >>> But, by the looks of the register content in my other mail, it seems as if >>> DMA0/IF1 can also use DDR2 Port 3. >>> >>> So, I think I want either >>> >>> A) the NAND controller to use DMAC0/IF0 (i.e. DDR2 port 1, and possibly 3) and >>> the LCDC to use master 9 (i.e. DDR2 Port 2) >>> >>> or >>> >>> B) the NAND controller to use DMAC1/IF1 (i.e. DDR2 port 2) and the LCDC to use >>> master 8 (i.e. DDR2 Port 3) >> >> Crap, that was not what I meant to express. Sorry for the confusion. This is >> better. >> >> So, I think I want either >> >> A) the NAND controller to use master 1 DMAC0/IF0 (i.e. slave 8 DDR2 port 2) and >> the LCDC to use master 9 (i.e. slave 9 DDR2 Port 3) >> >> or >> >> B) the NAND controller to use master 2 DMAC0/IF1 (i.e. slave 7 DDR2 port 1, and >> possibly slave 9 DDR2 port 3 (if my previous findings are relevant) and the >> LCDC to use master 8 (i.e. slave 8 DDR2 Port 2) >> >>> But, again, how do I limit DMAC0 to either of IF0 or IF1 for NAND accesses? >> >> So, I added a horrid patch (attached), which mainly adds printk lines, but >> additionally does one more thing in atc_prep_dma_memcpy. It changes the DSCR_IF >> field (from 0) to 1 for DMA-memcpy for dma0chan5 (i.e. the NAND). At least I >> think it does that? >> >> Running with that patch gets me this: >> >> # dmesg | grep -i dma >> at_hdmac ffffe600.dma-controller: Atmel AHB DMA Controller ( cpy set slave ), 8 channels >> at_hdmac ffffe800.dma-controller: Atmel AHB DMA Controller ( cpy set slave ), 8 channels >> dma dma0chan0: xlate 0 2 >> dma dma0chan1: xlate 0 2 >> at91_i2c f0014000.i2c: using dma0chan0 (tx) and dma0chan1 (rx) for DMA transfers >> dma dma1chan0: xlate 0 2 >> dma dma1chan1: xlate 0 2 >> at91_i2c f801c000.i2c: using dma1chan0 (tx) and dma1chan1 (rx) for DMA transfers >> dma dma0chan2: xlate 0 2 >> dma dma0chan3: xlate 0 2 >> dma dma0chan4: xlate 0 2 >> atmel_mci f0000000.mmc: using dma0chan4 for DMA transfers >> dma dma1chan2: xlate 0 2 >> dma dma1chan3: xlate 0 2 >> atmel_aes f8038000.aes: Atmel AES - Using dma1chan2, dma1chan3 for DMA transfers >> dma dma1chan4: xlate 0 2 >> atmel_sha f8034000.sha: using dma1chan4 for DMA transfers >> dma dma1chan5: xlate 0 2 >> dma dma1chan6: xlate 0 2 >> atmel_tdes f803c000.tdes: using dma1chan5, dma1chan6 for DMA transfers >> atmel-nand-controller 10000000.ebi:nand-controller: using dma0chan5 for DMA transfers >> dma dma0chan5: memcpy: 0 >> dma dma0chan5: DSCR_IF: 1 >> dma dma0chan5: memcpy: 1 >> >> So, output is as expected and I believe that the patch makes the NAND DMA >> accesses use master 2 DMAC0/IF1 and are thus forced to use slave 7 DDR2 Port 1 >> (and possibly 9). The LCDC is using slave 8 DDR2 Port 2. So there should be no >> slave conflict? >> >> But the on-screen crap remains during NAND accesses. >> >> But pressing on. >> >> I then changed the priorities for all accesses to 0 in the PRxSy registers, except >> the ones for masters 8/9 LCDC (slaves 8/9) which I left at priority 3. >> >> But the on-screen crap remains during NAND accesses. >> >> My guess is that the NAND DMA is doing too long bursts and that the LCDC therefore >> has to wait too long and simply fails to keep the pipeline from running short? >> >> So I tried to reduce the maximum SLOT_CYCLE for slaves 7 and 9 in the SCFGx >> registers. No noticeable effect either. >> >> I then tried to split bursts from master 2 (DMAC0/IF1) with small values in the >> MCFG2 register. No effect. >> >> I'm getting nowhere. > > Could it just be that you're reaching the DDR bus limit. As I said > previously, when you go through the CPU, and assuming you're consuming > the data directly, you have: > > 1/ NFC SRAM -> CPU > 2/ CPU -> L1 data cache --write-back--> DRAM > 3/ L1-cache -> CPU > > While, if you use DMA you get: > > 1/ NFC SRAM -> DRAM > 2/ SDRAM -> L1 data cache -> CPU > > So, if you're approaching the limit of (LP)DDR bandwidth, using the CPU > might make things a bit better. Still, if the limitation really comes > from the DDR bus, my opinion is that you should maybe use a smaller > resolution or use a more compact pixel format (RGB565?).
The issue is still there if I use a CLUT mode instead of rgb565, which is what I normally use (and what I would like to use, CLUT is just alien and a pain these days).
The panels we are using only supports one resolution (each), but the issue is there with both 1920x1080@16bpp and 1024x768@8bpp (~60Hz).
> Did you calculate how much of the bandwidth is taken by the HLCDC > block and compared it to the max (LP)DDR bandwidth?
I did, but don't remember the exact details. There is some room even for 1920x1080@16bpp, but not oceans of it. We were a bit uncertain if 16bpp would be possible, and in fact that was the reason I worked on CLUT support for atmel-hlcdc last year. But since the problem persists with much less memory pressure as well, I don't think that's it either.
Admittedly I have not tested these AHB matrix tricks with a smaller panel (it would take a bit of work to arrange for those tests), but the issue was there when I last tried (using defaults).
Cheers, Peter
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