On Wed, Oct 25, 2017 at 01:46:33PM -0600, Jason Gunthorpe wrote:

quoted

struct tpm_chip *tpm_chip_find_get(u64 id)
{
	struct tpm_chup *chip;
	struct tpm_chip *res = NULL;
	int chip_num = 0;
	int chip_prev;

	mutex_lock(&idr_lock);

	do {
		chip_prev = chip_num;

		chip = idr_get_next(&dev_nums_idr, &chip_num);

		if (chip && (!id || id == chip->id) && !tpm_try_get_ops(chip)) {
			res = chip;
			break;
		}
	} while (chip_prev != chip_num);

	mutex_unlock(&idr_lock);

	return res;
}

?? The old version was correct, idr_find_slowpath is better than an
idr_get_next serach if you already know id.

PrasannaKumar's solution seems right, if we already have chip, then we
just need to lock it again:

struct tpm_chip *tpm_chip_find_get(struct tpm_chip *chip)
{
	struct tpm_chip *res = NULL;

	mutex_lock(&idr_lock);

	if (!chip) {
		int chip_num = 0;
		int chip_prev;

		do {
			chip_prev = chip_num;
			chip = idr_get_next(&dev_nums_idr, &chip_num);
			if (chip && !tpm_try_get_ops(chip)) {
				res = chip;
				break;
			}
		} while (chip_prev != chip_num);
	} else {
		if (!tpm_try_get_ops(chip))
			res = chip;
	}

	mutex_unlock(&idr_lock);

	return res;
}

Jason

The id has a nice feature that it is unique for one boot cycle you can
even try to get a chip that has been deleted. It has the most stable
properties in the long run.

Address is a reusable identifier in one boot cycle.

/Jarkko
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