Re: [PATCH v3 19/23] ata: ahci: Add DWC AHCI SATA controller support

[Hannes Reinecke <hare@suse.de>]

On 5/12/22 01:18, Serge Semin wrote:
> Synopsys AHCI SATA controller can work pretty under with the generic
> AHCI-platform driver control. But there are vendor-specific peculiarities
> which can tune the device performance up and which may need to be fixed up
> for proper device functioning. In addition some DWC AHCI-based controllers
> may require small platform-specific fixups, so adding them in the generic
> AHCI driver would have ruined the code simplicity. Shortly speaking in
> order to keep the generic AHCI-platform code clean and have DWC AHCI
> SATA-specific features supported we suggest to add a dedicated DWC AHCI
> SATA device driver. Aside with the standard AHCI-platform resources
> getting, enabling/disabling and the controller registration the new driver
> performs the next actions.
> 
> First of all there is a way to verify whether the HBA/ports capabilities
> activated in OF are correct. Almost all features availability is reflected
> in the vendor-specific parameters registers. So the DWC AHCI driver does
> the capabilities sanity check based on the corresponding fields state.
> 
> Secondly if either the Command Completion Coalescing or the Device Sleep
> feature is enabled the DWC AHCI-specific internal 1ms timer must be fixed
> in accordance with the application clock signal frequency. In particular
> the timer value must be set to be Fapp * 1000. Normally the SoC designers
> pre-configure the TIMER1MS register to contain a correct value by default.
> But the platforms can support the application clock rate change. If that
> happens the 1ms timer value must be accordingly updated otherwise the
> dependent features won't work as expected. In the DWC AHCI driver we
> suggest to rely on the "aclk" reference clock rate to set the timer
> interval up. That clock source is supposed to be the AHCI SATA application
> clock in accordance with the DT bindings.
> 
> Finally DWC AHCI SATA controller AXI/AHB bus DMA-engine can be tuned up to
> transfer up to 1024 * FIFO words at a time by setting the Tx/Rx
> transaction size in the DMA control register. The maximum value depends on
> the DMA data bus and AXI/AHB bus maximum burst length. In most of the
> cases it's better to set the maximum possible value to reach the best AHCI
> SATA controller performance. But sometimes in order to improve the system
> interconnect responsiveness, transferring in smaller data chunks may be
> more preferable. For such cases and for the case when the default value
> doesn't provide the best DMA bus performance we suggest to use the new
> HBA-port specific DT-properties "snps,{tx,rx}-ts-max" to tune the DMA
> transactions size up.
> 
> After all the settings denoted above are handled the DWC AHCI SATA driver
> proceeds further with the standard AHCI-platform host initializations.
> 
> Note since DWC AHCI controller is now have a dedicated driver we can
> discard the corresponding compatible string from the ahci-platform.c
> module. The same concerns "snps,spear-ahci" compatible string, which is
> also based on the DWC AHCI IP-core.
> 
> Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
> 
> ---
> 
> Note there are three more AHCI SATA drivers which have been created for
> the devices based on the DWC AHCI SATA IP-core. It's AHCI SunXi, St and
> iMX drivers. Mostly they don't support the features implemented in this
> driver. So hopefully sometime in future they can be converted to be based
> on the generic DWC AHCI SATA driver and just perform some
> subvendor-specific setups in their own LLDD (glue) driver code. But for
> now let's leave the generic DWC AHCI SATA code as is. Hopefully the new
> DWC AHCI-based device drivers will try at least to re-use a part of the
> DWC AHCI driver methods if not being able to be integrated in the generic
> DWC driver code.
> 
> Changelog v2:
> - Change the local objects prefix from 'dwc_ahci_' to 'ahci_dwc_'.
>    (@Damien)
> ---
>   drivers/ata/Kconfig         |  10 +
>   drivers/ata/Makefile        |   1 +
>   drivers/ata/ahci_dwc.c      | 395 ++++++++++++++++++++++++++++++++++++
>   drivers/ata/ahci_platform.c |   2 -
>   4 files changed, 406 insertions(+), 2 deletions(-)
>   create mode 100644 drivers/ata/ahci_dwc.c
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		           Kernel Storage Architect
hare@suse.de			                  +49 911 74053 688
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