Re: [PATCH v2] ata: ahci: Add mask_port_map module parameter

[Niklas Cassel <cassel@kernel.org>]

On Fri, Apr 05, 2024 at 09:51:43PM +0900, Damien Le Moal wrote:
> Commits 0077a504e1a4 ("ahci: asm1166: correct count of reported ports")
> and 9815e3961754 ("ahci: asm1064: correct count of reported ports")
> attempted to limit the ports of the ASM1166 and ASM1064 AHCI controllers
> to avoid long boot times caused by the fact that these adapters report
> a port map larger than the number of physical ports. The excess ports
> are "virtual" to hide port multiplier devices and probing these ports
> takes time. However, these commits caused a regression for users that do
> use PMP devices, as the ATA devices connected to the PMP cannot be
> scanned. These commits have thus been reverted by commit 6cd8adc3e18
> ("ahci: asm1064: asm1166: don't limit reported ports") to allow the
> discovery of devices connected through a port multiplier. But this
> revert re-introduced the long boot times for users that do not use a
> port multiplier setup.
> 
> This patch adds the mask_port_map ahci module parameter to allow users
> to manually specify port map masks for controllers. In the case of the
> ASMedia 1166 and 1064 controllers, users that do not have port
> multiplier devices can mask the excess virtual ports exposed by the
> controller to speedup port scanning, thus reducing boot time.
> 
> The mask_port_map parameter accepts 2 different formats:
>  - mask_port_map=<mask>
>    This applies the same mask to all AHCI controllers
>    present in the system. This format is convenient for small systems
>    that have only a single AHCI controller.
>  - mask_port_map=<pci_dev>=<mask>,<pci_dev>=mask,...
>    This applies the specified masks only to the PCI device listed. The
>    <pci_dev> field is a regular PCI device ID (domain:bus:dev.func).
>    This ID can be seen following "ahci" in the kernel messages. E.g.
>    for "ahci 0000:01:00.0: 2/2 ports implemented (port mask 0x3)", the
>    <pci_dev> field is "0000:01:00.0".
> 
> When used, the kerenl messages indicate that a port map mask was forced.

Nit: s/kerenl/kernel/

> E.g.: without a mask:
> modrpobe ahci

Nit: s/modrpobe/modprobe/

> dmesg | grep ahci
> ...
> ahci 0000:00:17.0: AHCI vers 0001.0301, 32 command slots, 6 Gbps, SATA mode
> ahci 0000:00:17.0: (0000:00:17.0) 8/8 ports implemented (port mask 0xff)
> 
> With a mask:
> 
> modrpobe ahci mask_port_map=0000:00:17.0=0x1
> dmesg | grep ahci
> ...
> ahci 0000:00:17.0: masking port_map 0xff -> 0x1
> ahci 0000:00:17.0: AHCI vers 0001.0301, 32 command slots, 6 Gbps, SATA mode
> ahci 0000:00:17.0: (0000:00:17.0) 1/8 ports implemented (port mask 0x1)
> 
> Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
> ---

With nits fixed:
Reviewed-by: Niklas Cassel <cassel@kernel.org>