Messages in this thread Patch in this message | | | From | Alexandre Courbot <> | Date | Wed, 2 Mar 2016 19:36:23 +0900 | Subject | Re: [PATCH v2 2/2] mmc: sdhci-tegra: Specify valid DMA mask |
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On Wed, Mar 2, 2016 at 6:34 AM, Arnd Bergmann <arnd@arndb.de> wrote: > On Tuesday 01 March 2016 13:32:44 Alexandre Courbot wrote: >> On T210, the sdhci controller can address more than 32 bits of address >> space. Failing to express this fact results in the use of bounce >> buffers and affects performance. >> >> Signed-off-by: Alexandre Courbot <acourbot@nvidia.com> > > I don't get this one. Why don't you just set the (SDHCI_USE_SDMA | SDHCI_USE_ADMA) > flags that are checked in the first patch?
The test is against (!(host->flags & (SDHCI_USE_SDMA | SDHCI_USE_ADMA))), (see the '!') so it will be true (and the DMA mask will be set) if both flags are *not* set (why we set the mask to 64 bits here in that case, I don't know).
T210 is capable of SDMA, so we cannot use this condition for that purpose (maybe you missed the '!', in which case I understand why you were surprised).
> >> @@ -289,6 +291,7 @@ static const struct sdhci_tegra_soc_data soc_data_tegra20 = { >> .pdata = &sdhci_tegra20_pdata, >> .nvquirks = NVQUIRK_FORCE_SDHCI_SPEC_200 | >> NVQUIRK_ENABLE_BLOCK_GAP_DET, >> + .dma_mask = DMA_BIT_MASK(32), >> }; > > Can you describe what the specific bug is in these controllers? Do you mean they > support SDHCI_USE_SDMA or SDHCI_USE_ADMA in theory but you still have to prevent > them from using high addresses?
Ok, I think you probably missed the '!' then. :)
> >> @@ -353,6 +358,7 @@ static const struct sdhci_pltfm_data sdhci_tegra210_pdata = { >> >> static const struct sdhci_tegra_soc_data soc_data_tegra210 = { >> .pdata = &sdhci_tegra210_pdata, >> + .dma_mask = DMA_BIT_MASK(34), >> }; >> >> static const struct of_device_id sdhci_tegra_dt_match[] = { > > This one still completely weirds me out. What kind of odd limitation does > the controller have in Tegra 210? > > Are there actually any machines with more than 16GB?
It is not a limitation of the controller - I am just limiting the mask to the range of physical memory we can ever access on T210. My intent here is to overcome the default 32-bit mask, not to limit the range, so I could have set a 64-bit mask if not for my OCD. :P
But actually looking at how the various flags are interpreted in sdhci_add_host(), I see the following:
/* * It is assumed that a 64-bit capable device has set a 64-bit DMA mask * and *must* do 64-bit DMA. A driver has the opportunity to change * that during the first call to ->enable_dma(). Similarly * SDHCI_QUIRK2_BROKEN_64_BIT_DMA must be left to the drivers to * implement. */ if (caps[0] & SDHCI_CAN_64BIT) host->flags |= SDHCI_USE_64_BIT_DMA; Since this relies on what the hardware declares being capable of and is set on T210, I am very tempted to set a 64-bit dma_mask here and call it a day, but the above comment seems to suggest that this should have been done before.
If you think this is cool though, I will just do that and in conjunction with patch 1 this will do the job nicely.
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