linux-kernel - Re: [RFC PATCH 07/33] irqchip/gic-v3-its: Macro-ize its_send_single

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Date:   Fri, 17 Feb 2017 07:15:47 +0100
From:   Auger Eric <eric.auger@...hat.com>
To:     Marc Zyngier <marc.zyngier@....com>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Christoffer Dall <christoffer.dall@...aro.org>
Subject: Re: [RFC PATCH 07/33] irqchip/gic-v3-its: Macro-ize
 its_send_single_command



On 17/01/2017 11:20, Marc Zyngier wrote:
> Most ITS commands do operate on a collection object, and require
> a SYNC command to be performed on that collection in order to
> guarantee the execution of the first command.
> 
> With GICv4 ITS, another set of commands perform similar operations
> on a VPE object, and a VSYNC operations must be executed to guarantee
> their execution.
> 
> Given the similarities (post a command, perform a synchronization
> operation on a sync object), it makes sense to reuse the same
> mechanism for both class of commands.
> 
> Let's start with turning its_send_single_command into a huge macro
> that performs the bulk of the work, and a set of helpers that
> make this macro useeable for the GICv3 ITS commands.
s/useeable/usable
> 
> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
> ---
>  drivers/irqchip/irq-gic-v3-its.c | 82 ++++++++++++++++++++++------------------
>  1 file changed, 45 insertions(+), 37 deletions(-)
> 
> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> index 99f6130..520b764 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -484,43 +484,51 @@ static void its_wait_for_range_completion(struct its_node *its,
>  	}
>  }
>  
> -static void its_send_single_command(struct its_node *its,
> -				    its_cmd_builder_t builder,
> -				    struct its_cmd_desc *desc)
> -{
> -	struct its_cmd_block *cmd, *sync_cmd, *next_cmd;
> -	struct its_collection *sync_col;
> -	unsigned long flags;
> -
> -	raw_spin_lock_irqsave(&its->lock, flags);
> -
> -	cmd = its_allocate_entry(its);
> -	if (!cmd) {		/* We're soooooo screewed... */
> -		pr_err_ratelimited("ITS can't allocate, dropping command\n");
> -		raw_spin_unlock_irqrestore(&its->lock, flags);
> -		return;
> -	}
> -	sync_col = builder(cmd, desc);
> -	its_flush_cmd(its, cmd);
> -
> -	if (sync_col) {
> -		sync_cmd = its_allocate_entry(its);
> -		if (!sync_cmd) {
> -			pr_err_ratelimited("ITS can't SYNC, skipping\n");
> -			goto post;
> -		}
> -		its_encode_cmd(sync_cmd, GITS_CMD_SYNC);
> -		its_encode_target(sync_cmd, sync_col->target_address);
> -		its_fixup_cmd(sync_cmd);
> -		its_flush_cmd(its, sync_cmd);
> -	}
> -
> -post:
> -	next_cmd = its_post_commands(its);
> -	raw_spin_unlock_irqrestore(&its->lock, flags);
> -
> -	its_wait_for_range_completion(its, cmd, next_cmd);
> -}
> +#define __its_send_single_cmd(name, buildtype, synctype, buildfn)	\
> +void name(struct its_node *its,						\
> +	  buildtype builder,						\
> +	  struct its_cmd_desc *desc)					\
> +{									\
> +	struct its_cmd_block *cmd, *sync_cmd, *next_cmd;		\
> +	synctype *sync_obj;						\
> +	unsigned long flags;						\
> +									\
> +	raw_spin_lock_irqsave(&its->lock, flags);			\
> +									\
> +	cmd = its_allocate_entry(its);					\
Not related to this patch but I see that its_allocate_entry can spin for
up to 1s waiting for the ITS queue to drain. What are the circumstances
that can cause this? Also isn't it an issue in that case to hold the
spinlock for so long?

Thanks

Eric
> +	if (!cmd) {		/* We're soooooo screewed... */		\
> +		raw_spin_unlock_irqrestore(&its->lock, flags);		\
> +		return;							\
> +	}								\
> +	sync_obj = builder(cmd, desc);					\
> +	its_flush_cmd(its, cmd);					\
> +									\
> +	if (sync_obj) {							\
> +		sync_cmd = its_allocate_entry(its);			\
> +		if (!sync_cmd)						\
> +			goto post;					\
> +									\
> +		buildfn(sync_cmd, sync_obj);				\
> +		its_fixup_cmd(sync_cmd);				\
> +		its_flush_cmd(its, sync_cmd);				\
> +	}								\
> +									\
> +post:									\
> +	next_cmd = its_post_commands(its);				\
> +	raw_spin_unlock_irqrestore(&its->lock, flags);			\
> +									\
> +	its_wait_for_range_completion(its, cmd, next_cmd);		\
> +}
> +
> +static void its_build_sync_cmd(struct its_cmd_block *sync_cmd,
> +			       struct its_collection *sync_col)
> +{
> +	its_encode_cmd(sync_cmd, GITS_CMD_SYNC);
> +	its_encode_target(sync_cmd, sync_col->target_address);
> +}
> +
> +static __its_send_single_cmd(its_send_single_command, its_cmd_builder_t,
> +			     struct its_collection, its_build_sync_cmd)
>  
>  static void its_send_inv(struct its_device *dev, u32 event_id)
>  {
>